Plural form: multiple glasses or drinks that have been frosted (chilled or with a frosted rim), or instances of frosting coverage.
Plural of 'frosted,' the past participle of 'frost' used as a noun. In bartending and cooking, 'a frosted' means a drink with a chilled or crystalline rim, following standard English nominalization.
When bartenders frost the rim of a glass with sugar or salt, they're using the same word—'frosted'—as when water freezes, which shows how the same root word evolved to describe both natural ice and deliberate culinary decoration.
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