Good to put an end to slight obsession (5)
I believe the answer is:
thing
'obsession' is the definition.
(thesaurus)
'good to put an end to slight' is the wordplay.
'good' becomes 'g' (abbreviation).
'to put an end to' says to put letters next to each other (some letters appear at the end of another word).
'slight' becomes 'thin' ('thin' can be similar in meaning to 'slight'**).
'g' put after 'thin' is 'THING'.
(Other definitions for thing that I've seen before include "Obsession" , "An unnamed object or item" , "Unspecified object" , "Individual unit" , "Object, artefact" .)