flock (n.1) Look up flock at Dictionary.com
Old English flocc "a group of persons, company, troop," related to Old Norse flokkr "crowd, troop, band," Middle Low German vlocke "crowd, flock (of sheep);" of unknown origin, not found in other Germanic languages; perhaps related to folc "people," but the metathesis would have been unusual for Old English.

In Old English of humans only; extended c.1200 to "a number of animals of one kind moving or feeding together;" of domestic animals c.1300. The special reference to birds is recent (19c.). Transferred to bodies of Christians, in relation to Christ or their pastor, from mid-14c.
flock (n.2) Look up flock at Dictionary.com
"tuft of wool," mid-13c., also found in continental Germanic and Scandinavian, all probably from Old French floc, from Latin floccus "flock of wool, lock of hair."
flock (v.) Look up flock at Dictionary.com
c.1300 "gather, congregate" (intransitive), from flock (n.1). Related: Flocked; flocking.