Plural of compact; small cosmetic cases containing powder, foundation, or rouge; or formal agreements and treaties between parties.
From Latin compactus (joined together, agreed upon) from compingere (to join). The cosmetic sense emerged in the early 20th century; the legal sense dates back centuries.
A makeup compact is literally named for being 'compacted'—compressed tightly into a small space—but it's also a miniature of the legal concept: a small, neat agreement between you and your mirror!
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