Mordant
A substance capable of deepening the reaction to a stain (as in the pathology laboratory); incisive; burning or pungent; and so, by extension, biting and caustic in thought, manner, or style.</P> The word 'mordant' has some bite to it since it comes from the Latin 'mordere', the infinitive of the verb 'to bite.' In French 'mordant' means biting.