Conceit
Etymology
Formed in English from "conceive," on the model of "deceit" from "deceive," and ultimately from Latin concipere, "to take in, to conceive." Its first meaning was simply "a thought or notion" — a sense that survives in the "poetic conceit," an ingenious extended metaphor. The idea of a too-flattering notion of oneself narrowed that into the modern vice.
noun · /kun-SEET/
An excessively high opinion of one’s own worth or abilities.
What it names
The vice of overrating yourself — the settled belief that you are cleverer, better, or more important than you actually are.
Example
His conceit was such that he assumed the failed launch reflected the market’s dullness, not his design.
Related idea
Vanity craves admiration from others; conceit needs no audience — it is the private, inflated verdict a person passes on themselves.
noun · /kun-SEET/
An elaborate, extended metaphor that draws a surprising comparison and sustains it through a passage or whole work.
What it names
a literary device — the ingenious governing figure of a poem, as in the metaphysical poets
Example
Donne’s conceit likens two parted lovers to the legs of a drawing compass.
Related idea
Both senses come from “concept”: a striking idea one is pleased with. As a figure it is kin to allegory, but compressed into a single dazzling comparison rather than a whole coded story.