1560s, "violent encounter of armed forces or a pair of warriors," a military term, from French choc "violent attack," from Old French choquer "strike against," probably from Frankish, from a Proto-Germanic imitative base (compare Middle Dutch schokken "to push, jolt," Old High German scoc "jolt, swing").
Meaning "a sudden blow" is from 1610s; meaning "a sudden and disturbing impression on the mind" is from 1705. Sense of "feeling of being (mentally) shocked" is from 1876. Medical sense is attested from 1804 (it also once meant "seizure, stroke," 1794). Shock-absorber is attested from 1906 (short form shocks attested by 1961); shock wave is from 1907. Shock troops (1917) translates German stoßtruppen and preserves the word's original military sense. Shock therapy is from 1917; shock treatment from 1938.
"bundle of grain," early 14c., from Middle Low German schok "shock of corn," originally "group of sixty," from Proto-Germanic *skukka- (source also of Old Saxon skok, Dutch schok "sixty pieces; shock of corn;" German schock "sixty," Hocke "heap of sheaves"). In 16c.-17c. English the word sometimes meant "60-piece lot," from trade with the Dutch.
"thick mass of hair," 1819, from earlier shock (adj.) "having thick hair" (1680s), and a noun sense of "lap dog having long, shaggy hair" (1630s), from shough (1590s), the name for this type of dog, which was said to have been brought originally from Iceland; the word is perhaps from the source of shock (n.2), or from an Old Norse variant of shag (n.). Shock-headed Peter was used in 19c. translations for German Struwwelpeter.
"to come into violent contact, strike against suddenly and violently," 1570s, now archaic or obsolete, from shock (n.1). Meaning "to give (something) an electric shock" is from 1746; sense of "to offend, displease" is first recorded 1690s.