The most common and most likely answer to this crossword clue is the 9 letter word CONUNDRUM
I've seen this crossword clue in The Guardian
C
O
N
U
N
D
R
U
M
More clues leading to the result CONUNDRUM
- Riddle of sister tucking into fish and strong drink
- Sister devoured by fish – odd riddle
- Something fishy about sister with unusual problem
- Riddle of sister surrounded by fish and alcoholic drink
- Riddle posed by fish swallowing holy person given to drink
- Fish bites sister with drink problem
- Kid rings sister with unusual problem
- Kid getting a French tattoo is a poser
- Study a French instrument
- Fool holds sister with strange puzzle
Buddy explains!

The straight part
We know that "puzzle" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case puzzle = conundrum.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 CONUNDRUM mean?
CONUNDRUM noun- A difficult question or riddle, especially one using a play on words in the answer.
- A difficult choice or decision that must be made.