Enter unwanted suggestion, commonly coarse (7)
I believe the answer is:
intrude
'enter unwanted' is the definition.
'suggestion commonly coarse' is the wordplay.
'suggestion commonly' becomes 'int' (I am not sure about this - if you are sure you should believe this answer much more).
'coarse' becomes 'rude' (I've seen this before).
'int'+'rude'='INTRUDE'
(Other definitions for intrude that I've seen before include "Come in without invitation" , "Push in uninvited" , "Come in when not wanted" , "Untried (anag)" , "Trespass" .)