accentuator

(electronics) A circuit that provides for the first part of a process for increasing the strength of certain audio frequencies with respect to others, to help these frequencies override noise or to reduce distortion. Also known as accentuator circuit.
(materials) A material that acts to increase the selectivity or intensity of a stain.

A substance, such as aniline, that allows an otherwise impossible combination between a histologic element and a stain.