"soapy water churned into a froth," 1610s, see soap (n.) + suds.
Entries linking to soap-suds
soap n.
Middle English sope, from Old English sape "soap, salve," anciently 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 cleanse the 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 figurative meaning "flattery" is recorded from 1853.
suds n.
1540s, "dregs, leavings, muck," especially in East Anglia, "ooze left by flood" (according to OED this may be the original sense), perhaps borrowed from Middle Dutch sudse "marsh, bog," or related words in Frisian and Low German, cognate with Old English soden "boiled," from Proto-Germanic *suth-, from PIE *seut- "to seethe, boil" (see seethe). Meaning "soapy water" dates from 1580s; slang meaning "beer" first attested 1904. Related: Sudsy.