herdsman (n.)

"one employed in tending a herd of cattle," an alteration of Middle English herdman, from Old English heordman; see herd (n.1) + man (n.). The word was not common until the noun herd (n.2) in sense "keeper of domestic animals which go in herds" fell from use (compare shepherd). The unetymological -s- appeared early 15c., on model of craftsman, etc.