The most common and most likely answer to this crossword clue is the 10 letter word REGALEMENT
I've seen this crossword clue in The Daily Telegraph
R
E
G
A
L
E
M
E
N
T
Buddy explains!

The straight part
We know that "Feast" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case feast = regalement.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 REGALEMENT mean?
REGALEMENT noun- The act of regaling.