Something put on caught out of harmful habit (8)
I believe the answer is:
addition
'something put on' is the definition.
'caught out of harmful habit' is the wordplay.
'caught' becomes 'c' (cricket abbreviation).
'out of' is a deletion indicator.
'harmful habit' becomes 'addiction'.
'addiction' with 'c' taken out is 'ADDITION'.
(Other definitions for addition that I've seen before include "plus" , "Supplement" , "Simple kind of arithmetic" , "Combination of numbers to find the sum" , "Summing up process?" .)