The most common and most likely answer to this crossword clue is the 11 letter word SYMPATHISED
I've seen this crossword clue in The Daily Telegraph
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Buddy explains!
The straight part
We know that "Shared an understanding" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case shared an understanding = sympathised.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 SYMPATHISED mean?
SYMPATHISED verb- To have, show or express sympathy; to be affected by feelings similar to those of another, in consequence of knowing the person to be thus affected.
- To support, favour, have sympathy (with a political cause or movement, a side in a conflict / in an action).
- To say in an expression of sympathy.
- To have a common feeling, as of bodily pleasure or pain.
- To share (a feeling or experience).
- To agree; to be in accord; to harmonize.