Rotters hosting oddly dull do (7)
I believe the answer is:
swindle
'do' is the definition.
(thesaurus)
'rotters hosting oddly dull' is the wordplay.
'rotters' becomes 'swine' (swine can mean unpleasant people).
'hosting' indicates putting letters inside.
'oddly' indicates alternate letters.
The alternate letters of 'dull' are 'dl'.
'swine' going around 'dl' is 'SWINDLE'.
(Other definitions for swindle that I've seen before include "Cheat (out of money)" , "Scam" , "Bilk" , "Cheat; fraud" , "skin" .)