Is it ensure, insure, or assure?
1520s, cubbe "young fox," of unknown origin; perhaps from Old Irish cuib "whelp," or from Old Norse kobbi "seal." Extended to the young of bears, lions, etc., after 1590s. The native word was whelp. Cub Scout is from 1922.
: a cub reporter/ cub professornoun
[fr cub, ''the young of certain animals'']
A room or dwelling; pad: Let's go to my cub
[first form 1546+, second 1860s+; origin uncertain; related to Low German of the same meaning; the 1500s form refers to an animal's stall or shed; these senses are preserved more often in black English than in standard English]