1540, abbreviation of
videlicet "that is to say, to wit, namely" (1464), from L.
videlicet, contraction of
videre licet "it is permissible to see," from
videre "to see" (see
vision) +
licet "it is allowed," third person singular present indicative of
licere "be allowed." The
-z- is not a letter, but originally a twirl, representing the usual M.L. shorthand symbol for the ending
-et. "In reading aloud usually rendered by 'namely.' " [OED]