"very wet, abounding in moisture," 1823, from sop + -y (2). Meaning "sentimental" is attested by 1918. Related: Soppily; soppiness.
Entries linking to soppy
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).
-y 2
adjective suffix, "full of or characterized by," from Old English -ig, from Proto-Germanic *-iga- (source also of Dutch, Danish, German -ig, Gothic -egs), from PIE -(i)ko-, adjectival suffix, cognate with elements in Greek -ikos, Latin -icus (see -ic). Originally added to nouns in Old English; used from 13c. with verbs, and by 15c. even with other adjectives (for example crispy). Adjectives such as hugy, vasty are artificial words that exist for the sake of poetical metrics.