The most common and most likely answer to this crossword clue is the 7 letter word PLEDGED
I've seen this crossword clue in The Guardian
P
L
E
D
G
E
D
More clues leading to the result PLEDGED
Buddy explains!

The straight part
We know that "Promised/Promised" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case promised/promised = pledged.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 PLEDGED mean?
PLEDGED verb- To make a solemn promise (to do something).
- To deposit something as a security; to pawn.
- To give assurance of friendship by the act of drinking; to drink to one's health.