"to overspread," as with a fluid or tincture, "fill or cover," as with something fluid, 1580s, from Latin suffusus, past participle of suffundere "overspread, pour beneath, pour upon," from sub "under" (see sub-) + fundere "to pour" (from nasalized form of PIE root *gheu- "to pour"). Related: Suffused; suffusing.
word-forming element making adjectives from verbs, meaning "pertaining to, tending to; doing, serving to do," in some cases from Old French -if, but usually directly from Latin adjectival suffix -ivus (source also of Italian and Spanish -ivo). In some words borrowed from French at an early date it has been reduced to -y (as in hasty, tardy).
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<a href="https://www.etymonline.com/word/suffusive">Etymology of suffusive by etymonline</a>
Harper, D. (n.d.). Etymology of suffusive. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/suffusive