kestrel n.

kind of small falcon, windhover, c. 1600, earlier castrell (15c.), probably from Old French cresserele (13c.), earlier cercelle (Modern French crécelle), a word of obscure origin. Perhaps it is related to French crecerelle "rattle," from Latin crepitacillium "small rattle," diminutive of crepitaculum "noisy bell, rattle," from crepitare "to crackle, rattle;" possibly from the old belief that their noise frightened away other hawks. The unetymological -t- probably developed in French.