reniform (adj.)

"of or pertaining to the kidneys," 1650s, from French rénal and directly from Late Latin renalis "of or belonging to kidneys," from Latin ren (plural renes) "kidneys," a word of of uncertain etymology, with possible cognates in Old Irish aru "kidney, gland," Welsh arenn "kidney, testicle," Hittite hah(ha)ari "lung(s), midriff." Also possibly related are Old Prussian straunay, Lithuanian strėnos "loins," Latvian streina "loins." "The semantic shift from 'loins' to 'kidneys' is quite conceivable" [de Vaan].

word-forming element meaning "-like, -shaped, in the form of," from French -forme and directly from Latin -formis "-like, shaped," from forma "form" (see form (n.)). Properly preceded by an -i-.