Meteors, at times (4)
I believe the answer is:
ufos
'meteors at times' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for ufos that I've seen before include "Initially and formally, flying saucers" , "Supposed alien craft" , "Initially, formal flying saucers" , "Mysterious things" , "Supposed spaceships" .)