The most common and most likely answer to this crossword clue is the 10 letter word PROMISSORY
I've seen this crossword clue in The Times
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More clues leading to the result PROMISSORY
Buddy explains!
The straight part
We know that "for expressing commitment" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case for expressing commitment = promissory.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 PROMISSORY mean?
PROMISSORY adjective- Containing or consisting of a promise.
- (of a contractual provision) Stipulating the future actions required of the parties to an insurance policy or other business agreement.