The Collaborative International Dictionary of English v.0.48:

By \By\ (b[imac]), prep. [OE. bi, AS. b[imac], big, near to, by,
   of, from, after, according to; akin to OS. & OFries. bi, be,
   D. bij, OHG. b[imac], G. bei, Goth. bi, and perh. Gr. 'amfi`.
   E. prefix be- is orig. the same word. [root]203. See pref.
   Be-.]
   1. In the neighborhood of; near or next to; not far from;
      close to; along with; as, come and sit by me.
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            By foundation or by shady rivulet
            He sought them both.                  --Milton.
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   2. On; along; in traversing. Compare 5.
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            Long labors both by sea and land he bore. --Dryden.
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            By land, by water, they renew the charge. --Pope.
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   3. Near to, while passing; hence, from one to the other side
      of; past; as, to go by a church.
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   4. Used in specifying adjacent dimensions; as, a cabin twenty
      feet by forty.
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   5. Against. [Obs.] --Tyndale [1. Cor. iv. 4].
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   6. With, as means, way, process, etc.; through means of; with
      aid of; through; through the act or agency of; as, a city
      is destroyed by fire; profit is made by commerce; to take
      by force.
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   Note: To the meaning of by, as denoting means or agency,
         belong, more or less closely, most of the following
         uses of the word:
      (a) It points out the author and producer; as, "Waverley",
          a novel by Sir W.Scott; a statue by Canova; a sonata
          by Beethoven.
      (b) In an oath or adjuration, it indicates the being or
          thing appealed to as sanction; as, I affirm to you by
          all that is sacred; he swears by his faith as a
          Christian; no, by Heaven.
      (c) According to; by direction, authority, or example of;
          after; -- in such phrases as, it appears by his
          account; ten o'clock by my watch; to live by rule; a
          model to build by.
      (d) At the rate of; according to the ratio or proportion
          of; in the measure or quantity of; as, to sell cloth
          by the yard, milk by the quart, eggs by the dozen,
          meat by the pound; to board by the year.
      (e) In comparison, it denotes the measure of excess or
          deficiency; when anything is increased or diminished,
          it indicates the measure of increase or diminution;
          as, larger by a half; older by five years; to lessen
          by a third.
      (f) It expresses continuance or duration; during the
          course of; within the period of; as, by day, by night.
      (g) As soon as; not later than; near or at; -- used in
          expressions of time; as, by this time the sun had
          risen; he will be here by two o'clock.
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   Note: In boxing the compass, by indicates a pint nearer to,
         or towards, the next cardinal point; as, north by east,
         i.e., a point towards the east from the north;
         northeast by east, i.e., on point nearer the east than
         northeast is.
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   Note: With is used instead of by before the instrument with
         which anything is done; as, to beat one with a stick;
         the board was fastened by the carpenter with nails. But
         there are many words which may be regarded as means or
         processes, or, figuratively, as instruments; and
         whether with or by shall be used with them is a matter
         of arbitrary, and often, of unsettled usage; as, to a
         reduce a town by famine; to consume stubble with fire;
         he gained his purpose by flattery; he entertained them
         with a story; he distressed us with or by a recital of
         his sufferings. see With.
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   By all means, most assuredly; without fail; certainly.

   By and by.
      (a) Close together (of place). [Obs.] "Two yonge knightes
          liggyng [lying] by and by." --Chaucer.
      (b) Immediately; at once. [Obs.] "When . . . persecution
          ariseth because of the word, by and by he is
          offended." --Matt. xiii. 21.
      (c) Presently; pretty soon; before long.

   Note: In this phrase, by seems to be used in the sense of
         nearness in time, and to be repeated for the sake of
         emphasis, and thus to be equivalent to "soon, and
         soon," that is instantly; hence, -- less emphatically,
         -- pretty soon, presently.

   By one's self, with only one's self near; alone; solitary.

   By the bye. See under Bye.

   By the head (Naut.), having the bows lower than the stern;
      -- said of a vessel when her head is lower in the water
      than her stern. If her stern is lower, she is by the
      stern.

   By the lee, the situation of a vessel, going free, when she
      has fallen off so much as to bring the wind round her
      stern, and to take her sails aback on the other side.

   By the run, to let go by the run, to let go altogether,
      instead of slacking off.

   By the way, by the bye; -- used to introduce an incidental
      or secondary remark or subject.

   Day by day, One by one, Piece by piece, etc., each day,
      each one, each piece, etc., by itself singly or
      separately; each severally.

   To come by, to get possession of; to obtain.

   To do by, to treat, to behave toward.

   To set by, to value, to esteem.

   To stand by, to aid, to support.
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   Note: The common phrase good-by is equivalent to farewell,
         and would be better written good-bye, as it is a
         corruption of God be with you (b'w'ye).
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WordNet (r) 3.0 (2006):

by and by
    adv 1: at some eventual time in the future; "By and by he'll
           understand"; "I'll see you later" [syn: by and by,
           later]

Moby Thesaurus II by Grady Ward, 1.0:

32 Moby Thesaurus words for "by and by":
   after a time, after a while, afterward, afterwards, anon,
   before long, behind, betimes, by destiny, directly, ere long,
   fatally, hopefully, imminently, in a moment, in a while,
   in aftertime, in due course, in due time, in the future, infra,
   later, latterly, next, predictably, presently, probably, proximo,
   shortly, soon, subsequently, tomorrow



Easton's 1897 Bible Dictionary:

By and by
   immediately (Matt. 13:21; R.V., "straightway;" Luke 21:9).