Is it ensure, insure, or assure?
c.1300, "to direct one's mind or energies," from Old French atendre (12c., Modern French attendre) "to expect, wait for, pay attention," and directly from Latin attendere "give heed to," literally "to stretch toward," from ad- "to" (see ad-) + tendere "stretch" (see tenet). The notion is of "stretching" one's mind toward something. Sense of "take care of, wait upon" is from early 14c. Meaning "to pay attention" is early 15c.; that of "to be in attendance" is mid-15c. Related: Attended; attending.