1 See oar.
2 An effect of refraction in a light fog at sea which makes objects look larger than they are. ‘That ship looms large’, the dim outline of a vessel through fog and appearing larger than it in fact is. The same effect is often observed when the land is seen through a fog from seawards, cliffs frequently appearing much higher than they really are.
3 Also an effect of reflection on low cloud in the case of the light from a lighthouse or lightship, when the light itself cannot be seen directly.