c. 1300, coler, coller, "neck armor, gorget, something worn about the neck," from Old French coler "neck, collar" (12c., Modern French collier), from Latin collare "necklace, band or chain for the neck," from collum "the neck," from PIE *kwol-o- "neck" (source also of Old Norse and Middle Dutch hals "neck"), literally "that on which the head turns," from root *kwel- (1) "revolve, move round."
The spelling was re-Latinized in early modern English. From late 14c. as "border at the neck of a garment," also "band put around the neck of a dog or other animal for purposes of restraint or identification." From mid-15c. as "neck-band forming part of the harness of a horse or other draught-animal."
1550s, "to grab (someone) by the collar or neck," from collar (n.). Meaning "to capture" is attested from 1610s. Meaning "put a collar on" is from c. 1600. Related: Collared; collaring. As a past-participle adjective, collared "wearing a collar" is from late 14c.