sour or bitter in taste
harsh or corrosive in tone
"an acerbic tone piercing otherwise flowery prose"
"a barrage of acid comments"
"her acrid remarks make her many enemies"
"bitter words"
"blistering criticism"
"caustic jokes about political assassination, talk-show hosts and medical ethics"
"a sulfurous denunciation"
"a vitriolic critique"
Sour, bitter, and harsh to the taste, as unripe fruit.
The word comes from the Latin acerbus, which originally meant "sharp." It is related to the French word acerb.