viz.
1530s, abbreviation of videlicet
[2.] "that is to say, to wit, namely" (mid-15c.),
from Latin
videlicet, contraction of
videre licet [1.] "it is permissible to see,"
from
videre "to see" (see
vision) +
licet "it is allowed," third person singular present indicative of
licere "be allowed" (see
licence).
The -z- is not a letter, but originally a twirl, representing the usual Medieval Latin shorthand symbol for the ending -et. "In reading aloud usually rendered by 'namely.' " [OED]
