A costume or special outfit; the way someone is dressed; an unusual or eye-catching set of clothes.
From 'get up' (to dress oneself), a phrasal verb compound that became a noun. English frequently turns phrasal verbs into nouns for convenience.
The word 'getup' perfectly captures how English loves compounds: 'get up' (verb phrase) becomes 'getup' (noun), and you see this pattern everywhere—setup, breakup, makeup—showing how English constantly recycles itself.
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