Semantic drift
Etymology
From "semantic" (Greek "sēmantikos," significant, from "sēma," a sign) plus "drift," the imagery of slow, directionless movement. The concept is central to historical linguistics, which traces how usage nudges meaning step by step.
noun phrase · /si-MAN-tik drift/
The gradual change in a word’s meaning over time, often until it means something far from its origin.
What it names
A slow, cumulative process in language — meaning migrating across generations — that explains why old words so often surprise us.
Example
“Awful” once meant “awe-inspiring”; semantic drift turned it into a synonym for “terrible.”
Related idea
Not to be confused with semantic satiation, the fleeting sense that a word loses meaning when you repeat it many times in a row; satiation is a momentary perceptual glitch in one mind, while semantic drift is a permanent shift across a whole language. The word niceness is a classic case.