Origin and history of donnish

title of respect, 1520s, from Spanish or Portuguese Don, a title of respect prefixed to a man's Christian name, from Latin dominus "lord, master, owner" (from domus "house," from PIE root *dem- "house, household").

 It took on a general sense of "person of high importance or leading position," hence the English university sense "fellow of a college, any college authority" (c. 1660), originally student slang. The underworld sense is by 1952, from Italian don. The fem. form is Portuguese Dona, Spanish Doña, Italian Donna.

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.