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"smart" is also used as a crossword clue. If that's what you saw, the answer is often brainy (6 letters).
Definitions
capable of independent and apparently intelligent action
Word origin
From Middle English smerten, from Old English *smeortan (“to smart”), from Proto-West Germanic *smertan, from Proto-Germanic *smertaną (“to hurt, ache”), from Proto-Indo-European *(s)merd- (“to bite, sting”). Cognate with Scots smert, Dutch smarten, German schmerzen, Danish smerte, Swedish smärta.
Used in a sentence
“After being hit with a pitch, the batter exclaimed "Ouch, my arm smarts!"”
“A goad that […] smarts the flesh.”
“You think this cruel? take it for a rule, / No creature ſmarts ſo little as a Fool.”
Source: Wiktionary, CC BY-SA 4.0
Used as a crossword answer2 curated clues
01“Quick to learn”5 letters
02“Clever or stylish”5 letters
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