Is it farther or further?
1630s, from Latin caries "rottenness, decay," from Proto-Italic *kas-, usually said to be from PIE root *kere- "to injure, break apart" (cf. Greek ker "death, destruction," Old Irish krin "withered, faded"). Related: Carious. But de Vaan writes that "semantically, caries may just as well belong to careocared 'to lack' as 'defect, state of defectiveness' ...."
caries car·ies (kâr'ēz)
n. pl. caries
Decay of a bone or tooth, especially dental caries.