It's highly brilliant but not meteoric (5)
I believe the answer is:
comet
'highly brilliant but not meteoric' is the definition.
I can't tell whether this defines the answer.
'it's' is the wordplay.
I cannot really see how this works, but
'it' could be 't' (abbreviation. e.g. in 'tis) and 't' is present in the answer.
The remaining letters 'come' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for comet that I've seen before include "Tailed space traveller" , "Omen supposedly" , "Celestial body with luminous tail" , "body found in space" , "Heavenly body with a fiery tail" .)