decollation n.

active word-forming element in English and in many verbs inherited from French and Latin, from Latin de "down, down from, from, off; concerning" (see de), also used as a prefix in Latin, usually meaning "down, off, away, from among, down from," but also "down to the bottom, totally" hence "completely" (intensive or completive), which is its sense in many English words.

As a Latin prefix it also had the function of undoing or reversing a verb's action, and hence it came to be used as a pure privative — "not, do the opposite of, undo" — which is its primary function as a living prefix in English, as in defrost (1895), defuse (1943), de-escalate (1964), etc. In some cases, a reduced form of dis-.

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."

of women's fashionable dress, "low-necked," 1831, from French décolleté, past participle of décolleter "to bare the neck and shoulders," from dé- "off, away from" (see de-) + collet "collar of a dress," diminutive of col "neck," from Latin collum, from PIE root *kwel- (1) "revolve, move round."

By extension, of a dressed woman, "having the neck and shoulders exposed." Middle English had an equivalent and partially nativized adjective, decoloured (mid-15c.). Not to be confused with decollate (v.), which means "to behead" (see decollation).