Is it ensure, insure, or assure?
early 15c., from Middle French capacité "ability to hold" (15c.), from Latin capacitatem (nominative capacitas) "breadth, capacity, capability of holding much," noun of state from capax (genitive capacis) "able to hold much," from capere "to take" (see capable). Meaning "largest audience a place can hold" is 1908.
capacity ca·pac·i·ty (kə-pās'ĭ-tē)
The measure of potential cubic contents of a cavity or receptacle; volume.
Ability to perform or produce; capability.