Oxymoron
Etymology
From Greek oxýmōron, itself a fusion of oxýs ("sharp, keen") and mōrós ("dull, foolish") — so the word is quietly an example of the thing it names, "sharp-dull." Ancient rhetoricians prized the figure for compressing a paradox into two words, and the sense has held steady ever since.
noun · /ok-see-MOR-on/
A phrase that yokes two apparently contradictory terms — "deafening silence," "bittersweet."
What it names
The little jolt of a self-contradicting phrase that, held together, captures something a single word cannot — a tension made compact.
Example
The critic called the film "a modest blockbuster," an oxymoron that somehow summed it up perfectly.
Related idea
Paradox is a whole statement that seems self-contradictory yet may be true; an oxymoron is that contradiction squeezed into a single phrase.