el óleo - oil paint, oil painting
  el otoño - autumn, fall
  el obturador - camera shutter
  la oreja - ear (or a person or animal)
  oriental - eastern, Orient
  el orfebre, la orfebre - metalsmith, silversmith, goldsmith
  el oyente, la oyente - listener, member of an audience, one...
  el oso, la osa - bear
  la ortografía - spelling, orthography
  la oliva - olive
  ocasional - accidental, by chance, temporary,...
  la oruga - caterpillar
  oscuro - dark, obscure, overcast, uncertain,...
  el oro - gold
  la nevisca - snow flurry, light snowfall
  el neoyorquino, la neoyorquina - New Yorker, someone from New York
  el neonato, la neonata - newborn, neonate
  la necrología - obituary, obituary section of a...
  la noria - water wheel, Ferris wheel, big wheel...
  nulo - invalid, null and void