From WordNet (r) 3.0 (2006):
fog
n 1: droplets of water vapor suspended in the air near the
ground
2: an atmosphere in which visibility is reduced because of a
cloud of some substance [syn: fog, fogginess, murk,
murkiness]
3: confusion characterized by lack of clarity [syn: daze,
fog, haze]
v 1: make less visible or unclear; "The stars are obscured by
the clouds"; "the big elm tree obscures our view of the
valley" [syn: obscure, befog, becloud, obnubilate,
haze over, fog, cloud, mist]