Is it ensure, insure, or assure?
late 13c., "young man who attends a knight," later "member of the landowning class ranking below a knight" (c.1300), from Old French esquier "squire," literally "shield carrier" (see esquire). Meaning "country gentleman, landed proprietor" is from 1670s; as a general term of address to a gentleman, it is attested from 1828.
"to attend (a lady) as a gallant," late 14c., from squire (n.). Related: Squired; squiring.