Irish (n.) Look up Irish at Dictionary.com
c.1200, Irisce, from stem of Old English Iras "inhabitant of Ireland," from Old Norse irar, ultimately from Old Irish Eriu (accusative Eirinn, Erinn) "Erin," which is from Old Celtic *Iveriu (accusative *Iverionem, ablative *Iverione), perhaps from PIE *pi-wer- "fertile," literally "fat," from root *peie- "to be fat, swell" (see fat (adj.)).

Meaning "temper, passion" is 1834, American English (first attested in writings of Davy Crockett), from the legendary pugnacity of Irish people. Irish-American is from 1832; Irish stew is attested from 1814; Irish coffee is from 1950. Wild Irish (late 14c.) originally were those not under English rule; Black Irish in reference to those of Mediterranean appearance is from 1888.