Is it ensure, insure, or assure?
Old English nafela, nabula, from Proto-Germanic *nabalan (cf. Old Norse nafli, Danish and Swedish navle, Old Frisian navla, Middle Dutch and Dutch navel, Old High German nabalo, German Nabel), from PIE *(o)nobh- "navel" (cf. Sanskrit nabhila "navel, nave, relationship;" Avestan nafa "navel," naba-nazdishta "next of kin;" Persian naf; Latin umbilicus "navel;" Old Prussian nabis "navel;" Greek omphalos; Old Irish imbliu). For Romanic words, see umbilicus.
"Navel" words from other roots include Lithuanian bamba, Sanskrit bimba- (also "disk, sphere"), Greek bembix, literally "whirlpool." Old Church Slavonic papuku, Lithuanian pumpuras are originally "bud." Considered a feminine sexual center since ancient times, and still in parts of the Middle East, India, and Japan. In medieval Europe, it was averred that "[t]he seat of wantonness in women is the navel." [Cambridge bestiary, C.U.L. ii.4.26] Words for it in most languages have a secondary sense of "center." Meaning "center or hub of a country" is attested in English from late 14c. To contemplate (one's) navel "meditate" is from 1933; hence navel-gazer (1952); cf. omphaloskepsis. Navel orange attested from 1888.
navel na·vel (nā'vəl)
The mark on the surface of the abdomen that indicates where the umbilical cord was attached to the fetus during gestation. Also called bellybutton, umbilicus.