LATIN DICTIONARYLexicon Latīnum
suffixfirst/second-declension suffix

-gnus

-gnus (feminine -gna, neuter -gnum)
Classical[nʊs]Ecclesiastical[ɲus]

Meaning

  1. morphemesuffixsuffix forming adjectives denoting origin. born, originated from
    bene (“well”) + -gnus → benignus (“kind, generous”)
    male (“badly”) + -gnus → malignus (“ungenerous, grudging”)

Origins

From a combining form *-ǵn(h₁)-os from Proto-Indo-European *ǵenh₁- (“to produce, to beget, to give birth”), whence Latin gignō (“give birth”). Compare -genus, which was reformed from other forms.

Quick answers

What does -gnus mean in Latin?
-gnus, a suffix, means “suffix forming adjectives denoting origin. born, originated from”.
How do you pronounce -gnus?
In classical Latin, [nʊs]; in ecclesiastical (church) Latin, [ɲus].