mid-14c., overwhelmen, "to turn upside down, overthrow, knock over," from over- + Middle English whelmen "to turn upside down" (see whelm). Meaning "to submerge completely" is early 15c. Perhaps the connecting notion is a boat, etc., washed over, and overset, by a big wave. Figurative sense of "to bring to ruin" is attested from 1520s. Related: Overwhelmed; overwhelming; overwhelmingly.

mid-15c., "completely submerged or swamped," past-participle adjective from overwhelm. Figurative use by 1520s. Related: Overwhelmedness.

1953 (implied in underwhelming), a facetious play on overwhelm, with under. Related: Underwhelmed; underwhelmingly.

"overwhelm, sink (as if in a swamp)," 1772, from swamp (n.). Figurative sense is from 1818. Related: Swamped; swamping.

"overwhelm with delight or amazement," 1924, American English slang, from wow (interj.). Related: Wowed; wowing. Used as a noun meaning "unqualified success" since 1920.

1590s, "to pour over, overwhelm in a flood, inundate;" see deluge (n.). Figurative sense of "overrun like a flood, pour over in overwhelming numbers" is from 1650s. Related: Deluged; deluging.

late 14c., "render (a region or place) lonely by depopulation or devastation; lay waste, ruin," from desolate (adj.) or Latin desolatus. Meaning "overwhelm with grief, make sorry or weary by affliction" is from 1520s. Related: Desolated; desolating.

"overwhelm or confound with sudden surprise or wonder," 1580s, a back-formation from Middle English amased "stunned, dazed, bewildered," (late 14c.), earlier "stupefied, irrational, foolish" (c. 1200), from Old English amasod, from a- (1), probably used here as an intensive prefix, + *mæs (see maze). Related: Amazed; amazing.

mid-15c., "deadly, depriving of life," present-participle adjective from kill (v.). Meaning "overpowering, fascinating, attractive" is 1630s, from the verb in a figurative sense "overwhelm (someone) by strong effect on the mind or senses." Meaning "very powerful in effect, exceedingly severe, so as to (almost) kill one" is from 1844. Related: Killingly.

c. 1600 (transitive), from French submerger (14c.) or directly from Latin submergere "to plunge under, sink, overwhelm," from sub "under" (see sub-) + mergere "to plunge, immerse" (see merge). Intransitive meaning "sink under water, sink out of sight" is from 1650s, made common 20c. in connection with submarines. Related: Submerged; submerging.