"make a short, sharp, happy sound like a bird," mid-15c. (implied in chirping), echoic, or else a variant of Middle English chirken "to twitter" (late 14c.), from Old English cearcian "to creak, gnash." Related: Chirped. As a noun, attested from 1802.
the birds were chirping in the bushes
Chiron
chiropodist
chiropractic
chiropractor
chirosophy
chirp
chirpy
chirr
chirrup
chirurgeon
chisel