WordNet sense 1 (hang over, as of something threatening, dark, or menacing):

brood, loom, bulk large

WordNet sense 2 (be undecided about something; waver between conflicting positions or courses of action):

oscillate, vacillate, vibrate

WordNet sense 3 (move to and fro):

linger

WordNet sense 4 (be suspended in the air, as if in defiance of gravity):

levitate