Scottish (adj.)

Old English Scottas (plural) "inhabitants of Ireland, Irishmen," from Late Latin Scotti (c. 400), a name of uncertain origin, perhaps from Celtic (but answering to no known tribal name; Irish Scots appears to be a Latin borrowing). The name followed the Irish tribe which invaded Scotland 6c. C.E. after the Romans withdrew from Britain, and after the time of Alfred the Great the Old English word described only the Irish who had settled in the northwest of Britain.

adjectival word-forming element, Old English -isc "of the nativity or country of," in later use "of the nature or character of," from Proto-Germanic suffix *-iska- (cognates: Old Saxon -isk, Old Frisian -sk, Old Norse -iskr, Swedish and Danish -sk, Dutch -sch, Old High German -isc, German -isch, Gothic -isks), cognate with Greek diminutive suffix -iskos. In its oldest forms with altered stem vowel (French, Welsh). The Germanic suffix was borrowed into Italian and Spanish (-esco) and French (-esque). Colloquially attached to hours to denote approximation, 1916.

The -ish in verbs (abolish, establish, finish, punish, etc.) is a mere terminal relic from the Old French present participle.