Soggy comes from dialectal English sog ('a swamp, marsh; to soak') + -y, probably of Scandinavian origin and related to soak. The historical chain includes English sog. The quoted older sense, "a swamp, marsh; to soak," supplies the immediate semantic anchor for soggy. The formation is best read as suffixal and borrowed: the word soggy carries its older form-history into a compact English lexical shape. In present English it is used as a adj, "saturated with moisture; heavy and wet". English derivatives include soggily and sogginess. The result is a adj whose etymology preserves both the older form and the later English specialization.