The compound "three-liter" is a modern English formation combining the cardinal number "three" with the metric unit "liter". The word "three" has a deep Indo-European heritage, traceable to the PIE root tréyes, which evolved through Proto-Germanic into the Old English forms. "Liter" entered English via French in the late 18th century, ultimately derived from the Greek λίτρα, a term for a unit of weight. The compound logically and directly describes an engine's displacement or a container's volume by specifying the exact quantity of the standard unit, reflecting the precision of technical and automotive terminology.

Structure: three (number) + liter (unit of capacity) - three: From Old English þrīe, þrēo, from Proto-Germanic þrīz, from Proto-Indo-European tréyes. Functions as a cardinal number. - liter: From French litre, from Medieval Latin litra, from Ancient Greek λίτρα (lítra, "a Sicilian coin, a measure of weight"). Functions as a unit of volume/capacity.