May force (5)
I believe the answer is:
might
I believe this clue is a double definition.
'may' is the first definition.
('may' and 'might' are similar in meaning)
'force' is the second definition.
(might can mean power or force)
(Other definitions for might that I've seen before include "Capability" , "What functions as an auxiliary" , "- - and main" , "Clout" , "is not unlikely to" .)