Unvariable

Part of speech: adjective

Definitions

1. Describing something that stays the same and does not alter or fluctuate under any circumstances
2. Remaining constant and unchanging, never shifting in form, amount, or character over time
3. Not open to variation, so that it holds steady and cannot be modified from one instance to the next

Etymology: "Unvariable" is a plain formation: the prefix "un-", meaning "not," attached to "variable." The prefix descends from Old English "un-", which is one of the oldest and most productive negating elements in the language, and it has been used freely in English for centuries to reverse adjectives. "Variable" itself comes from Latin "variabilis," from "variare," "to change or diversify," which is the source of many English words built on the idea of difference and alteration. What makes this word unusual is its relationship to "invariable." Both mean "not changing," and English has ended up with two separate routes to the same sense. "Invariable" was formed from the Latin negating prefix "in-" and "variable," while "unvariable" combines the native English "un-" with the same base. Linguists call such pairs piecewise doublets, because each part of the word has been swapped for a different but equivalent piece, leaving two near-synonyms that share a root but took different paths into the language.