dumbstruck (adj.)

Old English dumb, of persons, "mute, silent, refraining from speaking or unable to speak," from Proto-Germanic *dumbaz "dumb, dull," which is perhaps from PIE *dheubh- "confusion, stupefaction, dizziness," from root *dheu- (1) "dust, mist, vapor, smoke," also expressing related notions of "defective perception or wits." The -b has probably been silent since 13c. Related: Dumbly; dumber; dumbest. Of animals, "lacking in speech," hence "without intellect" (c. 1200).

The fork in meaning probably comes via the notion of  "not responding through ignorance or incomprehension." The Old English, Old Saxon (dumb), Gothic (dumbs), and Old Norse (dumbr) forms of the word meant only "mute, speechless;" in Old High German (thumb) it meant both this and "stupid," and in Modern German this latter became the only sense (the sense of "mute, speechless" being expressed by stumm). Meaning "foolish, ignorant" was occasional in Middle English, but the modern use in this sense (since 1823) seems to be from influence of German dumm, especially in Pennsylvania German.

dumb-cake ..., n. A cake made in silence on St Mark's Eve, with numerous ceremonies, by maids, to discover their future husbands. [Century Dictionary]

Applied to silent contrivances, hence dumb-waiter. Dumb ox "stupid man" is by 1756; dumb-bunny "stupid person" is college slang from 1922; dumb blonde "woman seen as incapable of comprehending anything complicated" is by 1936.

Old English strican (past tense strac, past participle stricen) "pass lightly over, stroke, smooth, rub," also "go, move, proceed," from Proto-Germanic *strikan- (source also of Old Norse strykva "to stroke," Old Frisian strika, Middle Dutch streken, Dutch strijken "to smooth, stroke, rub," Old High German strihhan, German streichen), from PIE root *strig- "to stroke, rub, press" (see strigil). Related to streak and stroke, and perhaps influenced in sense development by cognate Old Norse striuka.

Sense of "to deal a blow" developed by early 14c.; meaning "to collide" is from mid-14c.; that of "to hit with a missile" is from late 14c. Meaning "to cancel or expunge" (as with the stroke of a pen) is attested from late 14c. A Middle English sense is preserved in strike for "go toward." Sense of "come upon, find" is from 1835 (especially in mining, well-digging, etc., hence strike it rich, 1854). Baseball sense is from 1853. To strike a balance is from the sense "balance accounts" (1530s).

Meaning "refuse to work to force an employer to meet demands" is from 1768, perhaps from notion of striking or "downing" one's tools, or from sailors' practice of striking (lowering) a ship's sails as a symbol of refusal to go to sea (1768), which preserves the verb's original sense of "make level, smooth."