c. 1200, Irisce, "of Irish nationality;" see Irish (n.). From 1580s as "Irish in nature or character." Irish stew is attested from 1814; Irish lace is from 1851; Irish coffee is from 1950.
Before 19c. often meaning "contradictory." In later use often in mocking or pejorative phrases, such as Irish apricot "potato," Irish daisy "common dandelion." Compare Dutch. Irish luck is by 1814, originally an ironic phrase indicating mischance or something done by means other than luck.
-ism
word-forming element making nouns implying a practice, system, doctrine, etc., from French -isme or directly from Latin -isma, -ismus (source also of Italian, Spanish -ismo, Dutch, German -ismus), from Greek -ismos, noun ending signifying the practice or teaching of a thing, from the stem of verbs in -izein, a verb-forming element denoting the doing of the noun or adjective to which it is attached. For distinction of use, see -ity. The related Greek suffix -isma(t)- affects some forms.