Encroach, force upon (6)
I believe the answer is:
impose
I believe this clue is a double definition.
'encroach' is the first definition.
(thesaurus)
'force upon' is the second definition.
(I've seen this before)
(Other definitions for impose that I've seen before include "Force (on someone)" , "Decree" , "Obtrude, force (on)" , "Put upon, say a tax" , "Levy or force upon" .)