Help one endlessly dispersing disinfectant (6)
I believe the answer is:
phenol
'disinfectant' is the definition.
(thesaurus)
'help one endlessly dispersing' is the wordplay.
'endlessly' means to remove the last letter.
'dispersing' is an anagram indicator.
'help'+'one'='helpone'
'helpone' with its last letter taken away is 'helpon'.
'helpon' is an anagram of 'PHENOL'.
(Other definitions for phenol that I've seen before include "Acidic substance" , "cleaner" , "No help (anag) - antiseptic" , "Carbolic acid" , "Powerful disinfectant" .)