international society of business women and women executives, first club formed 1921 in Oakland, Calif., U.S., from stem of sorority + optimist, probably after the Optimist Club.
1530s, "a society of women, body of women united for some purpose," from Medieval Latin sororitas "sisterhood, of or pertaining to sisters," from Latin soror "sister" (see sister). Sense of "women's society in a college or university" attested by 1887 (Alpha Delta Pi claims founding in 1851).
1759, "one who believes in metaphysical optimism," from French optimiste (1752); see optimism + -ist. Meaning "person of a hopeful disposition" is recorded by 1766.
