IPA: /ˈhɛdˌpiːs/
KK: /ˈhɛdˌpis/
An item worn on the head for protection, decoration, or as part of a costume.
She wore a beautiful headpiece made of flowers at the wedding.
Headpiece is formed from "head" (from Old English "heafod", meaning the upper part of the body or the leader) and "piece" (from Old French "piece", meaning a part or fragment). The word "headpiece" refers to a part that is worn on the head, often as an ornament or protective gear.
Think of the 'head' as the upper part of the body and 'piece' as a part of something — a headpiece is a part that goes on the head.