Tart, a.
Etymology: [AS. teart. 63. Cf. Tear, v. t.]
1. Sharp to the taste; acid; sour; as, a tart apple.
2. Fig.: Sharp; keen; severe; as, a tart reply; tart language; a tart rebuke. Why art thou tart, my brother Bunyan.
1 other Webster entry under this spelling
Tart, n.
A species of small open pie, or piece of pastry, containing jelly or conserve; a sort of fruit pie.
Shades of meaning
Fernald has no entry of its own for tart; he lists it under bitter.
Where he writes about it:
We say a sour face, sharp words, bitter complaints, caustic wit, cutting irony, biting sarcasm, a stinging taunt, harsh judgment, a tart reply. — from bitter
Tart and sharp utterances may not proceed from an intention to wound, but merely from a wit recklessly keen; cutting, stinging, and biting speech indicates more or less of hostile intent, the latter being the more deeply malicious. — from bitter