The Collaborative International Dictionary of English v.0.48:

Peep \Peep\ (p[=e]p), n.
   1. The cry of a young chicken; a chirp.
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   2. First outlook or appearance.
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            Oft have we seen him at the peep of dawn. --Gray.
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   3. A sly look; a look as through a crevice, or from a place
      of concealment.
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            To take t' other peep at the stars.   --Swift.
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   4. (Zool.)
      (a) Any small sandpiper, as the least sandpiper (Trigna
          minutilla).
      (b) The European meadow pipit (Anthus pratensis).
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   Peep show, a small show, or object exhibited, which is
      viewed through an orifice or a magnifying glass.

   Peep-o'-day boys, the Irish insurgents of 1784; -- so
      called from their visiting the house of the loyal Irish at
      day break in search of arms. [Cant]
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The Collaborative International Dictionary of English v.0.48:

Peep \Peep\ (p[=e]p), v. i. [imp. & p. p. Peeped (p[=e]pt); p.
   pr. & vb. n. Peeping.] [Of imitative origin; cf. OE. pipen,
   F. piper, p['e]pier, L. pipire, pipare, pipiare, D. & G.
   piepen. Senses 2 and 3 perhaps come from a transfer of sense
   from the sound which chickens make upon the first breaking of
   the shell to the act accompanying it; or perhaps from the
   influence of peek, or peak. Cf. Pipe.]
   1. To cry, as a chicken hatching or newly hatched; to chirp;
      to cheep.
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            There was none that moved the wing, or opened the
            mouth, or peeped.                     --Is. x. 14.
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   2. To begin to appear; to look forth from concealment; to
      make the first appearance; as, the sun peeped over the
      eastern hills.
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            When flowers first peeped, and trees did blossoms
            bear.                                 --Dryden.
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   3. To look cautiously or slyly; to peer, as through a
      crevice; to pry.
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            Peep through the blanket of the dark. --Shak.
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            From her cabined loophole peep.       --Milton.
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   Peep sight, an adjustable piece, pierced with a small hole
      to peep through in aiming, attached to a rifle or other
      firearm near the breech.
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WordNet (r) 3.0 (2006):

peep
    n 1: the short weak cry of a young bird [syn: cheep, peep]
    2: a secret look [syn: peek, peep]
    v 1: look furtively; "He peeped at the woman through the window"
    2: cause to appear; "he peeped his head through the window"
    3: make high-pitched sounds; "the birds were chirping in the
       bushes" [syn: peep, cheep, chirp, chirrup]
    4: speak in a hesitant and high-pitched tone of voice
    5: appear as though from hiding; "the new moon peeped through
       the tree tops"

Moby Thesaurus II by Grady Ward, 1.0:

91 Moby Thesaurus words for "peep":
   bend the eyes, blink, bug, cackle, call, carol, case, cast, caw,
   chatter, cheep, chip, chipper, chirk, chirm, chirp, chirr, chirrup,
   chitter, chuck, clack, cluck, cock-a-doodle-doo, complaint, coo,
   croak, cronk, crow, cuckoo, direct the eyes, drum, flash, gabble,
   gaggle, gander, glance, glimpse, gobble, grumble, guggle,
   half an eye, honk, hoo, hoot, look, look over,
   make a reconnaissance, meddle, murmur, nose, ogle, outcry, peek,
   peer, pip, pipe, play peekaboo, play the spy, protest,
   protestation, pry, put under surveillance, quack, quick sight,
   rapid glance, reconnoiter, roll, scold, scout, scout out, sing,
   slant, snoop, sound, spy, spy out, squawk, squeak, squiz,
   stake out, stare, take a peep, trill, tweedle, tweet, twit,
   twitter, warble, watch, whistle, wink