Is it ensure, insure, or assure?
1922, from sexy + -ness.
1905, from sex (n.) + -y (2). Originally "engrossed in sex;" sense of "sexually attractive" is 1923, first in reference to Valentino. An earlier word in this sense was sexful (1898). Related: Sexier; sexiest.
Very appealing; exciting; desirable; stimulating: Acid rain is politically sexy, but it hasn't half the allure of jobs (1970+)