The most common and most likely answer to this crossword clue is the 5 letter word IDIOT
I've seen this crossword clue in Financial Times
I
D
I
O
T
More clues leading to the result IDIOT
- One far from wise in Djibouti oddly
- In Djibouti, putting away every second mug
- I had nothing invested in it, being a fool
- Fool I spot holding electric current
- Simpleton’s one point taking one in
- One spot to smuggle in bit of Indian dope
- Wild, hit out regularly? Silly
- Stupid writer put one into end of sentence
- A halfwit or two seen around start of period
- First of all, I'm dismayed: I'm ostensibly the fool
Buddy explains!

The straight part
We know that "fool" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case fool = idiot.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 IDIOT mean?
IDIOT noun- A person of low general intelligence.
- A person who makes stupid decisions; a fool.
- A person of the lowest intellectual standing, a person who lacks the capacity to develop beyond the mental age of a normal four-year-old; a person with an IQ below 30.
- Idiotic, stupid