1559, "to strike, punch," which is probably from M.Du. dossen "beat forcefully." Meaning "to strike a sail in haste" is recorded from 1627; that of "to extinguish (a light)" is from 1785; perhaps influenced by dout (1526), an obsolete contraction of do out (cf. doff, don). OED regards the meaning "to throw water over" (1606) as a separate word, of unknown origin, though admitting there may be a connection of some sort.