The most common and most likely answer to this crossword clue is the 8 plus 5 letter word AMNIOTIC FLUID
I've seen this crossword clue in The Guardian
A
M
N
I
O
T
I
C
F
L
U
I
D
More clues leading to the result AMNIOTIC FLUID
Buddy explains!
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.