Like arty composition getting lost (6)
I believe the answer is:
astray
'lost' is the definition.
(synonyms)
'like arty composition getting' is the wordplay.
'like' becomes 'as' ().
'composition' indicates anagramming the letters.
'getting' indicates putting letters inside.
'arty' is an anagram of 'tray'.
'as' put into 'tray' is 'ASTRAY'.
(Other definitions for astray that I've seen before include "Off one's route or lost" , "Off-course" , "Missing, lost" , "wide of the mark" , "In a lost state" .)