Vicesimus

Part of speech: adjective

Definitions

1. The ordinal number representing the position of twentieth in a sequence or count
2. A term denoting the number relating to the twentieth item, often used in scholarly or mathematical contexts
3. An expression indicating the rank of twenty in a list or arrangement, particularly in formal or historical usage

Etymology: "Vicesimus" is the Latin ordinal "twentieth," built from "viginti," the Latin word for "twenty." The root "viginti" is a relative of Greek "eikosi" and English "twenty," which is itself a descendant of an older Germanic form that lost its initial sound in its own way over the centuries, so the two words share an ancestor but no obvious family resemblance on the surface. The ending "-esimus" is the Latin pattern used to form ordinal numbers above ten, so "vicesimus" follows the same logic as "undecimus" (eleventh) and "duodecimus" (twelfth). In Latin, the ending marks position in a sequence, which is why the word is essentially a counting label rather than a description of anything. English has borrowed this Latin form mostly in technical and institutional contexts. It appears in the word "vicesimal," meaning based on twenty, which is the adjective you would use for a number system built on that base. Its use is largely confined to scholarly writing and to the Latin naming of things such as the twentieth in a series of papal or regnal designations.