Plural of frilly; things that are frilly, flouncy, or elaborately decorated; sometimes used informally for women's delicate or decorative undergarments.
Plural of 'frilly' used as a noun, or derived from 'frill' + '-ies' suffix. The informal sense for undergarments is 20th-century British slang.
The word shows how slang often takes adjectives and turns them into nouns—'frillies' for fancy underwear is whimsical and humorous, the kind of colloquial term that lives in speech but rarely appears in formal writing, making it almost invisible to language history.
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