Is it ensure, insure, or assure?
"next after first," c.1300, from Old French second, secont, and directly from Latin secundus "following, next in time or order," also "secondary, subordinate, inferior," from root of sequi "follow" (see sequel). Replaced native other in this sense because of the ambiguousness of the earlier word. Second sight is from 1610s; an etymologically perverse term, because it means in reality the sight of events before, not after, they occur. Second fiddle first attested 1809:
A metaphor borrowed from a musical performer who plays the second or counter to one who plays the first or the "air." [Bartlett, "Dictionary of Americanisms," 1848]
"one-sixtieth of a minute of degree," also "sixtieth part of a minute of time," late 14c. in geometry, from Old French seconde, from Medieval Latin secunda, short for secunda pars minuta "second diminished part," the result of the second division of the hour by sixty (the first being the "prime minute," now called the minute), from Latin secunda, fem. of secundus (see second (adj.)). The second hand of a clock is attested from 1759.
1580s, "to support or represent in a duel, fight, etc.," from Middle French seconder, from Latin secundare "to assist, make favorable," from secundus "assisting, favorable, following, second" (see second (adj.)). The noun in this sense is first recorded 1580s. The verb in the parliamentary sense is first recorded 1590s. Related: Seconded; seconding.
second sec·ond2 (sěk'ənd)
Coming next after the first in order, place, rank, time, or quality.
Being the next closest to the innermost digit, especially on the foot.
fundamental unit of time, now defined in terms of the radiation frequency at which atoms of the element cesium change from one state to another.