Etymology tree Proto-Indo-European *h₂eḱ- Proto-Indo-European *-éh₁ti Proto-Indo-European *-yeti Proto-Indo-European *-éh₁yeti Proto-Indo-European *h₂eḱéh₁yeti Proto-Italic *akēō Latin aceō Proto-Indo-European *dʰeh₁-der. Proto-Italic *-iðos Latin -idus Latin acidusbor. French acidebor. English acid From French acide, from Latin acidus (“sour, acid”), from aceō (“to be sour”). Doublet of agita.