Is it ensure, insure, or assure?
1640s, "exert weight, move downward," from Modern Latin gravitatus, past participle of gravitare "gravitate," from Latin gravitas "heaviness, weight" (see gravity). Meaning "To be affected by gravity" is from 1690s. Figurative use from 1670s. Related: Gravitated; gravitating. The classical Latin verb was gravare "to make heavy, burden, oppress, aggravate."