ren.

Uncertain. Several etymologies proposed: * From Proto-Italic *hrēn, cognate with Ancient Greek φρήν (phrḗn, “heart, midriff, mind”), from Proto-Indo-European *gʷʰrḗn (“an internal part of the body”). (However, this involves uncertain sound changes: the regular outcome of word-initial Proto-Indo-European *gʷʰr- in Latin might instead have been fr-, as in frendo. Even if loss of labialization was regular, it is unclear whether *gʰr- normally became r- as in rāvus or gr- as in grāmen.) * Earlier *srēn, cognate with Old Prussian straunay, Lithuanian strė́nos, srė́nos f pl (“loins”), Latvian striena (“loins”) and Avestan 𐬭𐬁𐬥𐬀- (rāna-, “thigh”), from Proto-Indo-European *srḗn (“hip, loins”). Further disputed connection with Ancient Greek ῥάχις (rhákhis, “spine, chine”). (However, the word-medial evolution of *-sr- to -br- and the single example of frīgus from from Proto-Indo-European *sríHgos suggests that fr- is the expected word-initial outcome of original *sr-.) * Cognate with Tocharian A āriñc, Tocharian B arañce (“heart”) and Hittite 𒄩𒄩𒊑 (ḫa-ḫa-ri- /⁠ḫaḫri-⁠/, “lungs ~ midriff ?”) (exact meaning uncertain), from Proto-Indo-European *h₂eh₂-ri-, *h₂eh₂-r-en- (“an internal organ”). Compare also Old Irish áru and Welsh aren (“kidney”). * Less likely due to phonetic difficulties, continuing *regn(o)-, metathesized from earlier *negr(o)- (< *neɣr(o)-), related to Proto-Italic *neɣʷrō (“kidney, testicle”) (see there for related Latin words).