The most common and most likely answer to this crossword clue is the 5 letter word DOWER
I've seen this crossword clue in The Times
D
O
W
E
R
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The straight part
We know that "Widow’s share" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case widow’s share = dower.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does DOWER mean?
DOWER noun- The part of or interest in a deceased husband's property provided to his widow, usually in the form of a life estate.
- Property given by a groom directly to his bride at or before their wedding in order to legitimize the marriage; dowry.
- That with which one is gifted or endowed; endowment; gift.
- To give a dower or dowry.
- To endow.