single-file

The compound "single-file" is a transparent combination of two English words with Latin origins. "Single" derives from Latin singulus, meaning one or individual, which itself may trace back to a Proto-Indo-European root meaning "one". "File" originates from Latin filum, meaning a thread or string, a concept that evolved to denote a line or row of people or things, akin to beads on a string. The logic of the compound is perfectly literal: a "single file" is a line consisting of one thread or one column, directly preserving the ancient sense of filum as a guiding line. This imagery effectively conveys the modern meaning of objects or people arranged sequentially in one line.

Structure: single (one) + file (line) - single: From Latin singulus (one, individual). In this compound, it functions as a quantifier meaning "one". - file: From Latin filum (thread). In this compound, it functions as a noun meaning "line" or "row".