Put off by fellow cleaner (9)
I believe the answer is:
detergent
'cleaner' is the definition.
(chemical that cleans)
'put off by fellow' is the wordplay.
'put off' becomes 'deter' (both can mean to discourage).
'by' is a charade indicator (letters next to each other).
'fellow' becomes 'gent' (synonyms).
'deter'+'gent'='DETERGENT'
(Other definitions for detergent that I've seen before include "Cleaning product" , "Cleansing substance used for washing clothes" , "Soluble cleansing agent" , "Soluble cleanser" , "help with the washing-up" .)