Definition of "headlight"

A bright light, with a lens and reflector, on the front of a motor vehicle (or originally a ship or train), designed to illuminate the road when driving at night; normally one of a pair.  examples

(US, slang, vulgar, chiefly in the plural) A woman's breast.  quotations

(Canada, slang, vulgar, chiefly in the plural) A woman's erect nipples, partially masked by clothing.

(US, slang, chiefly in the plural) A jewel; especially a diamond.

(US, slang, chiefly in the plural) Lysergic acid diethylamide (LSD).