Mint factory is keeping going (8)
I believe the answer is:
millions
'mint' is the definition.
(thesaurus)
'factory is keeping going' is the wordplay.
'factory' becomes 'mill' (mill is a type of factory).
'keeping' is an insertion indicator (some letters kept inside).
'going' becomes 'on' (both can mean functioning or activated).
'is' going around 'on' is 'ions'.
'mill'+'ions'='MILLIONS'
(Other definitions for millions that I've seen before include "An amount this large could make Simon ill" , "Slim lino for large numbers" , "huge numbers" , "fortune?" .)