"soaked, drenched, very wet," 1877, present-participle adjective from sop (v.) "to drench with moisture."
Entries linking to sopping
sop n.
Middle English soppe, "something soaked," from Old English sopp- "bread soaked in water, wine, milk, or some other liquid" (in soppcuppe "cup into which sops are put"), from Proto-Germanic *supp-, which is related to Old English verb suppan (see sup (v.2)) and probably reinforced by Old French soupe (see soup (n.)). The meaning "something given to appease" is from 1660s, a reference to the sops given by the Sibyl to distract Cerberus in the "Aeneid." Also "dull or foolish person" (1620s).