late Old English cierlisc "of or pertaining to churls," from churl + -ish. Meaning "deliberately rude, surly and sullen" is late 14c. Related: Churlishly; churlishness.
Entries linking to churlish
churl n.
Old English ceorl "peasant, one of the lowest of freemen, man without rank," from Proto-Germanic *kerlaz, *karlaz (source also of Old Frisian zerl "man, fellow," Middle Low German kerle, Dutch kerel "freeman of low degree," German Kerl "man, husband," Old Norse karl "old man, man").
It had various meaning in early Middle English, including "man of the common people," "a country man," "husbandman," "free peasant;" by 1300, it meant "bondman, villain," also "fellow of low birth or rude manners."
For words for "common man" that acquire an insulting flavor over time, compare boor, villain. In this case, however, the same word also has come to mean "king" in many languages (such as Lithuanian karalius, Czech kral, Polish król) via Charlemagne.
-ish
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.