1. A reference to organisms that thrive in a bitter or pungent environment: An acidophilic microorganism grows well in a highly acrid medium.

A minute organism can be acidophilic in that it can or must live in a caustic situation (pH below 6).
2. Referring to anything that is easily stained with acid dye: Acidophilic tissue parts can be stained red by using the combination of crocein scarlet and acidic fuchsine dyes.