Lessens force: everything’s to follow (5)
I believe the answer is:
falls
'lessens' is the definition.
(I know this)
'force everything's to follow' is the wordplay.
'force' becomes 'f' (symbol used in Physics e.g. f=ma).
'everything's' becomes 'all's' (all things).
'to follow' is a charade indicator (letters next to each other) (some letters go after or follow others).
'f'+'alls'='FALLS'
(Other definitions for falls that I've seen before include "North Country force" , "Plummets" , "See 6 Down" , "Goes down" , "American seasons" .)