"stretched tight," 1670, from L. tensus, pp. of tendere "to stretch" (see tenet). Sense of "in a state of nervous tension" is first recorded 1821. The verb meaning "to make tense" is from 1676; intrans. sense of "to become tense" (often tense up) is recorded from 1946.
"form of a verb showing time of an action or state," early 14c., tens "time," also "tense of a verb" (late 14c.), from O.Fr. tens "time" (11c.), from L. tempus (see temporal).