A coronet is a small crown consisting of ornaments fixed on a metal ring. By one definition, a coronet differs from a crown in that a coronet never has arches, and from a tiara in that a coronet completely encircles the head, while a tiara does not. By a slightly different definition, a crown is worn by a king or queen, a coronet by a nobleman or lady. See also diadem.

The word stems from the Old French coronete, a diminutive of co(u)ronne ("crown"), itself from the Latin corona (also "wreath").

Traditionally, such headgear is – as indicated by the German equivalent Adelskrone (literally "crown of nobility") – used by nobles and by princes and princesses in their coats of arms, rather than by monarchs, for whom the word crown is customarily reserved in formal English, while many languages have no such terminological distinction. Other than a crown, a coronet shows the rank of the respective noble. Hence, in German there is also the term Rangkrone.

For equivalents, both physical and emblematic, in other languages and cultures, see under crown (headgear).