headpiece
A decorative type of headwear that is fitted around one's head (usually being fitted near/on the forehead) and doesn't fit the traditional definition of a crown, tiara, hairband, etc.
A headpiece can be worn with a hat, though it is usually worn on its own. Headpieces are usually depicted as jewelry, though it can be made out of nearly anything such as cloth, machinery, and so forth.

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