one-twentieth

The word is a modern English compound formed by directly combining the cardinal number "one" with the ordinal number "twentieth." This pattern for forming fractions (cardinal + ordinal) is consistent in English, as seen in "one-third" or "one-hundredth." The ordinal suffix "-th," used to form sequence numbers, derives from Proto-Germanic -dô and Proto-Indo-European -to-, a suffix forming verbal adjectives. In this construction, the literal meaning "the first of a series of twenty" logically evolves into the abstract mathematical concept of a single unit after a whole is divided into twenty equal portions.

Structure: one (1) + twentieth (ordinal of twenty) - one: From Old English 'ān', meaning the number 1. It functions as a cardinal number specifying the quantity. - twentieth: From Old English 'twēntigoþa', the ordinal form of 'twenty', meaning "constituting number twenty in a sequence." It functions as a fractional suffix, indicating division into twenty parts.