According to Coromines and Pascual, first attested in the 16th century. From the older agro, used until the 17th century, from Old Spanish agro, from Late Latin acrus, acra, acrum, from Classical Latin acer, acrem (“sharp, piercing, pungent”). Ultimately from Proto-Italic *akris, from Proto-Indo-European *h₂ḱrós (“sharp”).
The ending -io is due to influence from the Spanish verb agriar, or alternatively from a Vulgar Latin *acridus. Coromines and Pascual say that although agriar is not attested until the 18th century, they nevertheless suspect it may have existed much earlier. Related to Old Spanish agrión (“berro”), Mozarabic *aqriyûn (perhaps read *aqriyûl or *uqurión), Occitan agriota. Cognate with Old French aigre, Italian agro, Romanian acru.
- La toronja está muy agria. ― The grapefruit tastes very sour.
- Synonym: amargo
- (figuratively) bitter (said of a person)