The most common and most likely answer to this crossword clue is the 5 letter word NANAS
I've seen this crossword clue in The Guardian
N
A
N
A
S
More clues leading to the result NANAS
Buddy explains!

The straight part
We know that "fools" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case fools = nanas.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 NANAS mean?
NANAS noun- A banana
- A fool
- (term of endearment) one's grandmother
- A nanny