Excellent or first-rate; of superior quality or outstanding performance.
From 'bang' (meaning excellent, from the sound of impact suggesting forcefulness) plus 'up' (suggesting elevation or superiority). American slang originating in the late 19th/early 20th century.
The phrase 'bang-up' is a purely American invention that perfectly captures the enthusiastic, action-oriented spirit of early American English, where impact words became synonyms for excellence!
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