snobbish adj.

1781, "a shoemaker, a shoemaker's apprentice," a word of unknown origin. It is said to have been used in Cambridge University slang from c. 1796, often contemptuously, for "townsman, local merchant," and then passed into literary use, where by 1831 it meant "person of the ordinary or lower classes."

The meaning "person who vulgarly apes his social superiors" is by 1843, popularized 1848 by William Thackeray's "Book of Snobs." The meaning later broadened to include those who insist on their gentility, in addition to those who merely aspire to it, and by 1911 the word had its sense of "one who despises those who are considered inferior in rank, attainment, or taste" [OED], which reverses the sense of a century before. Inverted snob is from 1909:

Then there is that singular anomaly, the Inverted Snob, who balances a chip on his shoulder and thinks that everyone of wealth or social prominence is necessarily to be distrusted; that the rich are always pretentious and worldly, while those who have few material possessions are themselves possessed (like Rose Aylmer) of every virtue, every grace. [Atlantic Monthly, February 1922]

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.