amateurish adj.

1784, "one who has a taste for some art, study, or pursuit, but does not practice it," from French amateur "one who loves, lover" (16c., restored from Old French ameour), from Latin amatorem (nominative amator) "lover, friend," agent noun from amatus, past participle of amare "to love" (see Amy).

The meaning "one who cultivates and participates (in something) but does not pursue it professionally or with an eye to gain" (as opposed to professional) is from 1786; often with disparaging suggestions of "dabbler, dilettante," but not in athletics, where the disparagement shaded the professional, at least formerly. As an adjective, by 1838.

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.