Widow nervously entertaining holder of title (5)
I believe the answer is:
owner
'holder of title' is the definition.
(title can mean the right to ownership)
'widow nervously entertaining' is the wordplay.
'entertaining' indicates a hidden word.
'OWNER' is hidden within 'widow nervously'.
(Other definitions for owner that I've seen before include "The one in lawful possession" , "Title-holder" , "Title holder?" , "Man of property" , "One who possesses" .)