1530s, abbreviation of videlicet "that is to say, to wit, namely" (mid-15c.), from Latin 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" (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]

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Definitions of viz. from WordNet

viz. (adv.)
as follows;
Synonyms: namely / that is to say / to wit / videlicet