Base's chemical opposite (4)

I believe the answer is:

acid

(Other definitions for acid that I've seen before include "Type of chemical" , "Sharp - tart - kind of house party" , "Caustic liquid of many kinds" , "Morose" , "Hallucinogenic drug" .)

I've seen this clue in the LA Times.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.