c.1300, "safe, secure," later "mentally certain" (c.1450), from O.Fr.
sur, seur "safe, secure," from L.
securus "free from care, untroubled, heedless, safe" (see
secure). Pronunciation development followed that of
sugar. As an affirmative meaning "yes, certainly" it dates from 1803, from M.E. meanings "firmly established, having no doubt," and phrases like
to be sure (1657),
sure enough (1545), and
for sure (1586). The use as a qualifier meaning "assuredly" goes back to 1425.
Sure-footed is from 1633;
sure-fire first attested 1901;
sure thing dates from 1836. In 16c.-17c.,
Suresby was an appellation for a person to be depended upon.