'dandy' originates from English slang in the late 18th century, possibly influenced by Scots 'dandie' or as a pet form of the name 'Andrew', though its exact origin is uncertain.

'dandy' appeared in late 18th-century English to mean a fashionable or showy man; the word was used in literature and periodicals and retained the modern form 'dandy'.

Initially, it meant 'a fashionable, often ostentatious man', and over time it kept that sense while also developing an informal adjectival and exclamatory sense meaning 'fine' or 'excellent'.