dandy (n.)
c. 1780, of uncertain origin; it first appeared in a Scottish border ballad:
I've heard my granny crack
O' sixty twa years back
When there were sic a stock of Dandies O
etc. In that region, Dandy is diminutive of Andrew (as it was in Middle English generally). The word was in vogue in London c. 1813-1819. His female counterpart was a dandizette (1821) with French-type ending.
dandy (adj.)
1792, from dandy (n.). Very popular c. 1880-1900. Related: Dandified; dandify.