The most common and most likely answer to this crossword clue is the 5 plus 2 letter word KNEES UP
K
N
E
E
S
U
P
More clues leading to the result KNEES UP
Buddy explains!
The straight part
We know that "riotous party" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case riotous party = knees up.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 KNEES UP mean?
KNEES UP noun- A party.