Singular lady's providing force for lawman (7)
I believe the answer is:
sheriff
'lawman' is the definition.
(sheriff is a kind of lawman)
'singular lady's providing force' is the wordplay.
'singular' becomes 's' (abbreviation sometimes used in dictionaries).
'lady' becomes 'her' (I've seen this before).
'providing' becomes 'if' (I've seen this in other clues).
'force' becomes 'F' (symbol used in Physics e.g. f=ma).
's'+'her'+'if'+'f'='SHERIFF'
'for' acts as a link.
(Other definitions for sheriff that I've seen before include "Crown executive officer in a county (England and Wales) - judge (Scotland) - lawman (US)" , "American lawman" , "Chief officer of the Crown in a county" , "US law enforcement officer" , "US county law enforcer" .)