Artist leaves out one moon of Saturn (5)
I believe the answer is:
titan
'moon of saturn' is the definition.
(Titan is a moon of Saturn)
'artist leaves out one' is the wordplay.
I cannot really see how this works, but
'one' could be 'an' (an apple is one apple) and 'an' is located in the answer.
The remaining letters 'tit' 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).
(Other definitions for titan that I've seen before include "Giant god of Greek myth" , "Jolly large figure" , "bigwig" , "Person of heroic stature" , "Old giant" .)