The Collaborative International Dictionary of English v.0.48:

Enter- \En"ter-\ [F. entre between, fr. L. inter. See Inter-]
   A prefix signifying between, among, part.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Enter \En"ter\, v. t. [imp. & p. p. Entered; p. pr. & vb. n.
   Entering.] [OE. entren, enteren, F. entrer, fr. L. intrare,
   fr. intro inward, contr. fr. intero (sc. loco), fr. inter in
   between, between. See Inter-, In, and cf. Interior.]
   1. To come or go into; to pass into the interior of; to pass
      within the outer cover or shell of; to penetrate; to
      pierce; as, to enter a house, a closet, a country, a door,
      etc.; the river enters the sea.
      [1913 Webster]

            That darksome cave they enter.        --Spenser.
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            I, . . . with the multitude of my redeemed,
            Shall enter heaven, long absent.      --Milton.
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   2. To unite in; to join; to be admitted to; to become a
      member of; as, to enter an association, a college, an
      army.
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   3. To engage in; to become occupied with; as, to enter the
      legal profession, the book trade, etc.
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   4. To pass within the limits of; to attain; to begin; to
      commence upon; as, to enter one's teens, a new era, a new
      dispensation.
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   5. To cause to go (into), or to be received (into); to put
      in; to insert; to cause to be admitted; as, to enter a
      knife into a piece of wood, a wedge into a log; to enter a
      boy at college, a horse for a race, etc.
      [1913 Webster]

   6. To inscribe; to enroll; to record; as, to enter a name, or
      a date, in a book, or a book in a catalogue; to enter the
      particulars of a sale in an account, a manifest of a ship
      or of merchandise at the customhouse.
      [1913 Webster]

   7. (Law)
      (a) To go into or upon, as lands, and take actual
          possession of them.
      (b) To place in regular form before the court, usually in
          writing; to put upon record in proper from and order;
          as, to enter a writ, appearance, rule, or judgment.
          --Burrill.
          [1913 Webster]

   8. To make report of (a vessel or her cargo) at the
      customhouse; to submit a statement of (imported goods),
      with the original invoices, to the proper officer of the
      customs for estimating the duties. See Entry, 4.
      [1913 Webster]

   9. To file or inscribe upon the records of the land office
      the required particulars concerning (a quantity of public
      land) in order to entitle a person to a right pf
      pre["e]mption. [U.S.] --Abbott.
      [1913 Webster]

   10. To deposit for copyright the title or description of (a
       book, picture, map, etc.); as, "entered according to act
       of Congress."
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   11. To initiate; to introduce favorably. [Obs.] --Shak.
       [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Enter \En"ter\, v. i.
   1. To go or come in; -- often with in used pleonastically;
      also, to begin; to take the first steps. "The year
      entering." --Evelyn.
      [1913 Webster]

            No evil thing approach nor enter in.  --Milton.
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            Truth is fallen in the street, and equity can not
            enter.                                --Is. lix. 14.
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            For we which have believed do enter into rest.
                                                  --Heb. iv. 3.
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   2. To get admission; to introduce one's self; to penetrate;
      to form or constitute a part; to become a partaker or
      participant; to share; to engage; -- usually with into;
      sometimes with on or upon; as, a ball enters into the
      body; water enters into a ship; he enters into the plan;
      to enter into a quarrel; a merchant enters into
      partnership with some one; to enter upon another's land;
      the boy enters on his tenth year; to enter upon a task;
      lead enters into the composition of pewter.
      [1913 Webster]

   3. To penetrate mentally; to consider attentively; -- with
      into.
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            He is particularly pleased with . . . Sallust for
            his entering into internal principles of action.
                                                  --Addison.
      [1913 Webster]

WordNet (r) 3.0 (2006):

enter
    v 1: to come or go into; "the boat entered an area of shallow
         marshes" [syn: enter, come in, get into, get in,
         go into, go in, move into] [ant: exit, get out,
         go out, leave]
    2: become a participant; be involved in; "enter a race"; "enter
       an agreement"; "enter a drug treatment program"; "enter
       negotiations" [syn: enter, participate] [ant: chuck up
       the sponge, drop by the wayside, drop out, fall by the
       wayside, give up, quit, throw in, throw in the
       towel]
    3: register formally as a participant or member; "The party
       recruited many new members" [syn: enroll, inscribe,
       enter, enrol, recruit]
    4: be or play a part of or in; "Elections figure prominently in
       every government program"; "How do the elections figure in
       the current pattern of internal politics?" [syn: figure,
       enter]
    5: make a record of; set down in permanent form [syn: record,
       enter, put down]
    6: come on stage
    7: take on duties or office; "accede to the throne" [syn:
       accede, enter]
    8: put or introduce into something; "insert a picture into the
       text" [syn: insert, infix, enter, introduce]
    9: set out on (an enterprise or subject of study); "she embarked
       upon a new career" [syn: embark, enter]

Moby Thesaurus II by Grady Ward, 1.0:

213 Moby Thesaurus words for "enter":
   admit, affiliate, affiliate with, appear, arise, associate,
   balance, balance the books, barge in, be admitted, become manifest,
   become visible, begin, book, break in, breeze in, burst in,
   bust in, calendar, capitalize, carry, carry over, carve,
   cast up accounts, catalog, chalk, chalk up, charge off, check in,
   chronicle, close out, close the books, combine, come,
   come barging in, come breezing in, come busting in, come forth,
   come forward, come in, come in sight, come into, come out,
   come to hand, come to light, commence, countersign, credit,
   creep in, crop out, cross the threshold, crowd in, cut, debit,
   docket, document, drop in, ease in, edge in, embark in, embark on,
   embark upon, emerge, engage in, engrave, enlist, enroll, enscroll,
   enter into, enter on, enter upon, enumerate, fade in, file,
   fill out, gain admittance, get in, get into, go in, go into, grave,
   have an entree, have an in, heave in sight, hop in, impanel,
   incise, index, infiltrate, infuse, ingress, inject, inoculate,
   inscribe, insert, insinuate, intercalate, interject, interpolate,
   introduce, intromit, intrude, invade, inventory, irrupt, issue,
   issue forth, itemize, jam in, join, join up, jot down, journalize,
   jump in, keep books, keep score, league with, list, log,
   look forth, look in, loom, make a memorandum, make a note,
   make an entry, make out, mark down, materialize, matriculate,
   minute, note, note down, offer, outcrop, pack in, participate in,
   pass into, peep out, penetrate, perfuse, pierce, pigeonhole,
   place upon record, poll, pop in, post, post up, present, press in,
   probe, proffer, program, puncture, push in, put down, put in,
   put in writing, put on paper, put on tape, rear its head, record,
   reduce to writing, register, rise, schedule, score, see the light,
   set, set down, set foot in, set in, show, show up, sign, sign on,
   sign up, slip in, sneak in, squeeze in, start, step in, stick in,
   stream forth, strike a balance, strike the eye, submit, tabulate,
   take down, take in, take out membership, take up,
   take up membership, tally, tape, tape-record, team up with,
   team with, tender, throw in, thrust in, tuck in, turn up,
   undertake, videotape, visit, wedge in, whip in, work in, write,
   write down, write in, write out, write up