Is it ensure, insure, or assure?
masc. proper name, from Latin dexter "on the right hand" (see dexterity). Cf. also Benjamin.
dexter dex·ter (děk'stər)adj. Of or located on the right side.
A despised person who is a zealous student, computer user, etc; chiphead, propeller head: A dexter, that's your asi nerd, dork, or pud (1980s+ Teenagers)