The Collaborative International Dictionary of English v.0.48:

Cheep \Cheep\ (ch[=e]p), v. i. [imp. & p. p. Cheeped
   (ch[=e]pt).] [Cf. Chirp].
   To chirp, as a young bird.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Cheep \Cheep\, v. t.
   To give expression to in a chirping tone.
   [1913 Webster]

         Cheep and twitter twenty million loves.  --Tennyson.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Cheep \Cheep\, n.
   A chirp, peep, or squeak, as of a young bird or mouse.
   [1913 Webster]

WordNet (r) 3.0 (2006):

cheep
    n 1: the short weak cry of a young bird [syn: cheep, peep]
    v 1: make high-pitched sounds; "the birds were chirping in the
         bushes" [syn: peep, cheep, chirp, chirrup]

Moby Thesaurus II by Grady Ward, 1.0:

45 Moby Thesaurus words for "cheep":
   cackle, call, carol, caw, chatter, chip, chipper, chirk, chirm,
   chirp, chirr, chirrup, chitter, chuck, clack, cluck,
   cock-a-doodle-doo, coo, croak, cronk, crow, cuckoo, drum, gabble,
   gaggle, gobble, guggle, honk, hoo, hoot, peep, pip, pipe, quack,
   roll, scold, sing, squawk, trill, tweedle, tweet, twit, twitter,
   warble, whistle