Left single and solitary (4)
I believe the answer is:
lone
'solitary' is the definition.
('lone' can be a synonym of 'solitary')
'left single' is the wordplay.
'left' becomes 'l' (common abbreviation).
'single' becomes 'one' (I've seen this before).
'l'+'one'='LONE'
'and' is the link.
(Other definitions for lone that I've seen before include "The ... Ranger, fictional masked cowboy" , "Companionless" , "Unaccompanied" , "Solitary or single" , "Solitary, without companions" .)