acid

English acid comes from French acide, which comes from Latin acidus, meaning 'sour, acid.' That Latin word traces to the verb aceō, 'to be sour.'

The word stayed close to its root meaning throughout — from the Latin verb for being sour, to the adjective describing sourness, to English's borrowing of that same quality.

Acid is a doublet of agita, meaning both words descend from the same root through different paths.