Old English sape "soap, salve" (originally a reddish hair dye used by Germanic warriors to give a frightening appearance), from Proto-Germanic *saipon "dripping thing, resin" (source also of Middle Low German sepe, West Frisian sjippe, Dutch zeep, Old High German seiffa, German seife "soap," Old High German seifar "foam," Old English sipian "to drip"), from PIE *soi-bon-, from root *seib- "to pour out, drip, trickle" (perhaps also the source also of Latin sebum "tallow, suet, grease").
Romans and Greeks used oil to clean skin; the Romance words for "soap" (Italian sapone, French savon, Spanish jabon) are from Late Latin sapo "pomade for coloring the hair" (first mentioned in Pliny), which is a Germanic loan-word, as is Finnish saippua. The meaning "flattery" is recorded from 1853.
Soap opera is recorded from 1939, as a disparaging reference to daytime radio dramas sponsored by soap manufacturers.
word-forming element denoting "belonging to, of the nature of," from Latin -aceus, enlarged form of adjectival suffix -ax (genitive -acis); see -acea. Especially in biology, "pertaining to X order of plants or animals."
<a href="https://www.etymonline.com/word/saponaceous">Etymology of saponaceous by etymonline</a>
Harper, D. (n.d.). Etymology of saponaceous. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/saponaceous