1) Baby bird 2) Frog or fledgling 3) Hatchling, or eye 4) Keyhole snoop 5) Looker 6) Nestling 7) Newborn nestling, at times 8) Peeping tom 9) Slangy detective 10) Slang for eye 11) Small frog 12) Small tree frog 13) Species of frog 14) Spectator 15) Viewer 16) Voyeur 17) Watcher 18) Witness 19) Young bird 1) Chick 2) Eye 3) Frog 4) Snoop 5) Spier 6) Toad 7) Voyeur 
• (n.) One who peeps; a prying person; a spy. • (n.) The eye; as, to close the peepers. • (n.) A chicken just breaking the shell; a young bird.
Peep'er noun 1. A chicken just breaking the shell; a young bird. 2. One who peeps; a prying person; a spy. « Who's there? peepers , . . . eavesdroppers?» J. Webster. 3. The eye; as, to close the peepers . [ Colloq.]
Peeper is slang for eye.
[n] - an animal that makes short high-pitched sounds
noun an animal that makes short high-pitched sounds