Displease by leaving conclusion (6)
I believe the answer is:
offend
'displease' is the definition.
(thesaurus)
'by leaving conclusion' is the wordplay.
'by' says to put letters next to each other.
'leaving' becomes 'off' (I've seen this in other clues).
'conclusion' becomes 'end' (end is a kind of conclusion).
'off'+'end' is 'OFFEND'.
(Other definitions for offend that I've seen before include "Insult - act criminally" , "Affront - break the law" , "Distress" , "tread on someone's toes?" , "Outrage" .)