Entries related to soft-soap
From c. 1200 of material things, "not stiff, not coarse, fine; yielding to weight." From late 14c. of wind, rain, etc. Of sounds, "quiet, not loud," from early 13c. Of words, "mild, restrained; courteous" mid-14c. From late 14c. as "indulgent," also "physically feeble; easily overcome, lacking manly courage." From 1755 of water ("relatively free from mineral salts"), from 1789 of coal. Meaning "foolish, simple, silly" is attested from 1620s; earlier "easily moved or swayed; soft-hearted, sympathetic; docile" (early 13c.). In reference to drinks, "non-alcoholic" from 1880. As an adverb, Old English softe "gently;" late 13c. as "quietly." As an interjection from 1540s.
Soft landing is from 1958 and the U.S. space program. Adjective soft-core (in reference to pornography) is from 1966 (see hardcore). Soft rock as a music style is attested from 1969. Soft sell is from 1955. Soft-shoe as a dancing style is attested from 1927. Soft-boiled is from 1757 of eggs; of persons, ideas, etc., 1930 (compare half-baked). Soft-focus (adj.) of camera shots is from 1917. The softer sex "women collectively" is from 1640s.
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" (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.