The most common and most likely answer to this crossword clue is the 10 letter word EXPLAINING
I've seen this crossword clue in The Daily Telegraph
E
X
P
L
A
I
N
I
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G
More clues leading to the result EXPLAINING
Buddy explains!
The straight part
We know that "Serving as an excuse for why it was" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case serving as an excuse for why it was = explaining.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 EXPLAINING mean?
EXPLAINING verb- To make plain, manifest, or intelligible; to clear of obscurity; to illustrate the meaning of.
- To give a valid excuse for past behavior.
- To make flat, smooth out.
- To unfold or make visible.
- To make something plain or intelligible.
- Explanation