is from 1889, Amer.Eng., from situation of a beaten prizefighter. Down home (adj.) is 1931, Amer.Eng.; down the hatch as a toast is from 1931; down to the wire is 1901, from horse-racing. Down time is from 1952. Down under "Australia and New Zealand" attested from 1886; Down East "Maine" is from 1825.
"soft feathers," c.1369, from O.N. dunn, perhaps ult. from PIE base *dheu- "to fly about (like dust), to whirl, shake."
O.E. dun "hill," from Celtic word for "hill, citadel" (cf. O.Ir. dun "hill, hill fort," and second element in place names London, Verdun, etc.), from PIE base *dheue- "to close, finish, come full circle" (cf. O.E. dun "hill," M.Du. dune "sandy hill"). Meaning "elevated rolling grassland" is from c.1300.