shear (n.) Look up shear at Dictionary.com
"act of clipping," 1610s, also as a unit of measure of the age of a sheep, from shear (v.). Scientific and mechanical sense "type of strain" is from 1850.
shear (v.) Look up shear at Dictionary.com
Old English sceran, scieran (class IV strong verb; past tense scear, past participle scoren) "to cleave, hew, cut with a sharp instrument; cut (hair); shear (sheep)," from Proto-Germanic *skero "to cut" (source also of Old Norse and Old Frisian skera, Dutch scheren, German scheren "to shear"), from PIE root *sker- (1) "to cut."