noun, feminine/ɛ.ɡʁœʁ/plural: aigreurs
sourness (sour flavor); bitterness (bitter emotion)
“1864, Rudolf Charles, Preface to Testament by Jean Meslier, page 14” — He attacked us, openly in his own essays, hoping thereby to draw out an ill-considered response from us which, by its bitterness and the spirit of the attack, would compromise the cause of progress in general and ourselves in particular.
From aigre + -eur.