"act of striking," c. 1300, probably from Old English *strac "stroke," from Proto-Germanic *straik- (source also of Middle Low German strek, German streich, Gothic striks "stroke"); see stroke (v.).
The meaning "mark of a pen" is from 1560s; that of "a striking of a clock" is from mid-15c. Sense of "feat, achievement" (as in stroke of luck, 1853) first found 1670s; the meaning "single pull of an oar or single movement of machinery" is from 1731. Meaning "apoplectic seizure" is from 1590s (originally the Stroke of God's Hand). Swimming sense is from 1800.