With words of acceptance, married: later so alone (7)
'later so alone' is the definition.
(alone after the death of a spouse)
'with words of acceptance married' is the wordplay.
'with' becomes 'w' (abbreviation).
'words of acceptance' becomes 'I do' (vow said to accept a husband or wife).
'married' becomes 'wed' (similar in meaning).
(Another definition for widowed that I've seen is "Having lost one's spouse".)