The Collaborative International Dictionary of English v.0.48:

To \To\ (?, emphatic or alone, ?, obscure or unemphatic), prep.
   [AS. t[=o]; akin to OS. & OFries. t[=o], D. toe, G. zu, OHG.
   zuo, zua, z[=o], Russ. do, Ir. & Gael. do, OL. -do, -du, as
   in endo, indu, in, Gr. ?, as in ? homeward. [root]200. Cf.
   Too, Tatoo a beat of drums.]
   1. The preposition to primarily indicates approach and
      arrival, motion made in the direction of a place or thing
      and attaining it, access; and also, motion or tendency
      without arrival; movement toward; -- opposed to from.
      "To Canterbury they wend." --Chaucer.
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            Stay with us, go not to Wittenberg.   --Shak.
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            So to the sylvan lodge
            They came, that like Pomona's arbor smiled.
                                                  --Milton.
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            I'll to him again, . . .
            He'll tell me all his purpose.
            She stretched her arms to heaven.     --Dryden.
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   2. Hence, it indicates motion, course, or tendency toward a
      time, a state or condition, an aim, or anything capable of
      being regarded as a limit to a tendency, movement, or
      action; as, he is going to a trade; he is rising to wealth
      and honor.
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   Note: Formerly, by omission of the verb denoting motion, to
         sometimes followed a form of be, with the sense of at,
         or in. "When the sun was [gone or declined] to rest."
         --Chaucer.
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   3. In a very general way, and with innumerable varieties of
      application, to connects transitive verbs with their
      remoter or indirect object, and adjectives, nouns, and
      neuter or passive verbs with a following noun which limits
      their action. Its sphere verges upon that of for, but it
      contains less the idea of design or appropriation; as,
      these remarks were addressed to a large audience; let us
      keep this seat to ourselves; a substance sweet to the
      taste; an event painful to the mind; duty to God and to
      our parents; a dislike to spirituous liquor.
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            Marks and points out each man of us to slaughter.
                                                  --B. Jonson.
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            Whilst they, distilled
            Almost to jelly with the act of fear,
            Stand dumb and speak not to him.      --Shak.
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            Add to your faith virtue; and to virtue knowledge;
            and to knowledge temperance; and to temperance
            patience; and to patience godliness; and to
            godliness brotherly kindness; and to brotherly
            kindness charity.                     --2 Pet. i.
                                                  5,6,7.
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            I have a king's oath to the contrary. --Shak.
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            Numbers were crowded to death.        --Clarendon.
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            Fate and the dooming gods are deaf to tears.
                                                  --Dryden.
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            Go, buckle to the law.                --Dryden.
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   4. As sign of the infinitive, to had originally the use of
      last defined, governing the infinitive as a verbal noun,
      and connecting it as indirect object with a preceding verb
      or adjective; thus, ready to go, i.e., ready unto going;
      good to eat, i.e., good for eating; I do my utmost to lead
      my life pleasantly. But it has come to be the almost
      constant prefix to the infinitive, even in situations
      where it has no prepositional meaning, as where the
      infinitive is direct object or subject; thus, I love to
      learn, i.e., I love learning; to die for one's country is
      noble, i.e., the dying for one's country. Where the
      infinitive denotes the design or purpose, good usage
      formerly allowed the prefixing of for to the to; as, what
      went ye out for see? (--Matt. xi. 8).
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            Then longen folk to go on pilgrimages,
            And palmers for to seeken strange stranders.
                                                  --Chaucer.
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   Note: Such usage is now obsolete or illiterate. In colloquial
         usage, to often stands for, and supplies, an infinitive
         already mentioned; thus, he commands me to go with him,
         but I do not wish to.
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   5. In many phrases, and in connection with many other words,
      to has a pregnant meaning, or is used elliptically. Thus,
      it denotes or implies:
      (a) Extent; limit; degree of comprehension; inclusion as
          far as; as, they met us to the number of three
          hundred.
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                We ready are to try our fortunes
                To the last man.                  --Shak.
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                Few of the Esquimaux can count to ten. --Quant.
                                                  Rev.
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      (b) Effect; end; consequence; as, the prince was flattered
          to his ruin; he engaged in a war to his cost; violent
          factions exist to the prejudice of the state.
      (c) Apposition; connection; antithesis; opposition; as,
          they engaged hand to hand.
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                Now we see through a glass, darkly; but then
                face to face.                     --1 Cor. xiii.
                                                  12.
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      (d) Accord; adaptation; as, an occupation to his taste;
          she has a husband to her mind.
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                He to God's image, she to his was made.
                                                  --Dryden.
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      (e) Comparison; as, three is to nine as nine is to
          twenty-seven; it is ten to one that you will offend
          him.
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                All that they did was piety to this. --B.
                                                  Jonson.
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      (f) Addition; union; accumulation.
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                Wisdom he has, and to his wisdom, courage.
                                                  --Denham.
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      (g) Accompaniment; as, she sang to his guitar; they danced
          to the music of a piano.
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                Anon they move
                In perfect phalanx to the Dorian mood
                Of flutes and soft recorders.     --Milton.
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      (h) Character; condition of being; purpose subserved or
          office filled. [In this sense archaic] "I have a king
          here to my flatterer." --Shak.
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                Made his masters and others . . . to consider
                him to a little wonder.           --Walton.
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   Note: To in to-day, to-night, and to-morrow has the sense or
         force of for or on; for, or on, (this) day, for, or on,
         (this) night, for, or on, (the) morrow. To-day,
         to-night, to-morrow may be considered as compounds, and
         usually as adverbs; but they are sometimes used as
         nouns; as, to-day is ours.
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               To-morrow, and to-morrow, and to-morrow;
               Creeps in this petty pace from day to day.
                                                  --Shak.
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   To and again, to and fro. [R.]

   To and fro, forward and back. In this phrase, to is
      adverbial.
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            There was great showing both to and fro. --Chaucer.
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   To-and-fro, a pacing backward and forward; as, to commence
      a to-and-fro. --Tennyson.

   To the face, in front of; in behind; hence, in the presence
      of.

   To wit, to know; namely. See Wit, v. i.
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   Note: To, without an object expressed, is used adverbially;
         as, put to the door, i. e., put the door to its frame,
         close it; and in the nautical expressions, to heave to,
         to come to, meaning to a certain position. To, like on,
         is sometimes used as a command, forward, set to. "To,
         Achilles! to, Ajax! to!" --Shak.
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WordNet (r) 3.0 (2006):

to and fro
    adv 1: moving from one place to another and back again; "he
           traveled back and forth between Los Angeles and New
           York"; "the treetops whipped to and fro in a frightening
           manner"; "the old man just sat on the porch and rocked
           back and forth all day" [syn: back and forth, backward
           and forward, to and fro]

Moby Thesaurus II by Grady Ward, 1.0:

32 Moby Thesaurus words for "to and fro":
   alternately, back and forth, backward and forward,
   backwards and forwards, by turns, capriciously, changeably,
   desultorily, erratically, every other, hitch and hike, in and out,
   in rotation, in turns, inconstantly, make and break,
   mutatis mutandis, off and on, on and off, reciprocally,
   ride and tie, round and round, seesaw, shuttlewise, turn about,
   uncertainly, unsteadfastly, unsteadily, up and down, variably,
   vice versa, waveringly