To dress up, decorate, or make something look fancier or more attractive, usually followed by 'up'.
American slang from the early 1900s, origin uncertain—possibly from the name Gussie (a pet name for Augusta or Gustave) or influenced by other slang terms. The meaning evolved from theatrical and vernacular contexts.
The existence of 'gussy up' in American slang shows how ordinary names can become verbs: we don't know exactly why 'Gussie' stuck, but once it did, English speakers applied it universally to mean 'fancy up.'
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