Is it ensure, insure, or assure?
late 14c., "action of founding," from Old French fondacion (14c.) or directly from Latin fundationem (nominative fundatio) "a founding," noun of action from past participle stem of fundare (see found (v.1)). The Latin word is glossed in Old English by staþol. Meaning "that which is founded" (a college, hospital, etc.) is from 1510s; meaning "funds endowed" is early 15c. Sense of "solid base of a structure" is from late 15c.
foundation foun·da·tion (foun-dā'shən)
The basis on which something stands or is supported; a base.