Is it ensure, insure, or assure?
Old English eanian "to bring forth" (young), especially in reference to sheep or goats, from Proto-Germanic *agwnojanan (cf. Dutch oonen), perhaps from PIE *agwhnos "lamb" (cf. Greek amnos "lamb," Latin agnus, Old Church Slavonic agne, Old Irish van, Welsh oen). Yeanling "young lamb, kid" is recorded from 1630s.