False promise lacking right force (6)
I believe the answer is:
impose
'force' is the definition.
(thesaurus)
'false promise lacking right' is the wordplay.
'false' indicates an anagram.
'lacking' is a deletion indicator.
'right' becomes 'r' (common abbreviation).
'promise' with 'r' taken away is 'pomise'.
'pomise' anagrammed gives 'IMPOSE'.
(Other definitions for impose that I've seen before include "Force (something) to be done or accepted" , "Inflict (something unpleasant)" , "Foist" , "Obtrude, force (on)" , "Put or lay on- say a tax" .)