The compound adjective "three-cylinder" is a transparent modern English formation, combining a native Germanic numeral with a classical geometric and mechanical term. "Three" originates from the Proto-Indo-European root trei-, which gave rise to the numeral across many Indo-European languages, signifying a fundamental quantity. "Cylinder" entered English via Latin from the Greek kulindros, a word describing a rolling object, derived from the verb kulindein (to roll). In mechanical engineering, a cylinder refers to the chamber in which a piston moves. Thus, the term's logic is straightforwardly descriptive: it literally denotes an engine or apparatus configured with three such cylindrical piston chambers.

Structure: three (number) + cylinder (geometric shape/engine component) - three: From Old English þrīe, of Germanic origin; related to Dutch drie and German drei, from an Indo-European root shared by Latin tres and Greek treis. Functions as a numerical quantifier. - cylinder: From Latin cylindrus, from Greek kulindros 'roller, cylinder', from kulindein 'to roll'. Functions as the core noun denoting the specific object or component.