Enter by force (6)
I believe the answer is:
invade
'enter by force' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for invade that I've seen before include "Overrun" , "Enter with armed forces to attack" , "Enter a country by force with an army" , "Intrude on" , "make unwelcome advances" .)