late 14c., "fresh green color," from Old French verdure "greenness, greenery, green fields, herbs," from verd, variant of vert "green" (12c.), from Latin viridis (source of Spanish, Italian verde), related to virere "be green," of unknown origin. Perhaps ultimately from a root meaning "growing plant" and cognate with Lithuanian veisti "propagate," Old Norse visir "bud, sprout," Old English wise "sprout, stalk, etc." But de Vaan writes that "None of the adduced set of cognates (Lat. 'green', Baltic 'multiply, fruit', Gm. 'sprout, meadow') undoubtedly belong together." Meaning "green plants, vegetation" is attested from c. 1400.
variant of suffix -an (q.v.), with connective -i-. From Latin -ianus, in which the -i- originally was from the stem of the word being attached but later came to be felt as connective. In Middle English frequently it was -ien, via French.
<a href="https://www.etymonline.com/word/viridian">Etymology of viridian by etymonline</a>
Harper, D. (n.d.). Etymology of viridian. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/viridian