The most common and most likely answer to this crossword clue is the 10 letter word FORBEARING
I've seen this crossword clue in The Daily Telegraph
F
O
R
B
E
A
R
I
N
G
More clues leading to the result FORBEARING
Buddy explains!

The straight part
We know that "Understanding" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case understanding = forbearing.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 FORBEARING mean?
FORBEARING noun- Forbearance; restraint
- To keep away from; to avoid; to abstain from.
- To refrain from proceeding; to pause; to delay.
- To refuse; to decline; to withsay; to unheed.
- To control oneself when provoked.
- Characterized by patience and indulgence; long-suffering