acerb UK /əˈsɜːb/US /əˈsɜɹb/ adjective2 •(no longer used) Sour, bitter, and harsh to the taste, such as unripe fruit.If you put Spirit of Sulphur to the Peruvian Bark, it then becomes very acerb. If you mix Mercury with Spirit of Nitre or Oil of Vitriol whilst it boils, it then is very acerb. — 1732 •(figurative, no longer used) Sharp and harsh in expressing oneself.As to the somewhat acerb remarks of the member for Jacques Cartier, I may pass them over […] — 1909 formsacerber · more acerb · acerbest · most acerb