The most common and most likely answer to this crossword clue is the 5 letter word DUMMY
I've seen this crossword clue in The Guardian
D
U
M
M
Y
Buddy explains!
The straight part
We know that "Idiot" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case idiot = dummy.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 DUMMY mean?
DUMMY noun- A silent person; a person who does not talk.
- An unintelligent person.
- A figure of a person or animal used by a ventriloquist; a puppet.
- Something constructed with the size and form of a human, to be used in place of a person.
- A person who is the mere tool of another; a man of straw.
- A deliberately nonfunctional device or tool used in place of a functional one.
- A "dummy teat"; a plastic or rubber teat used to soothe or comfort a baby; a pacifier.
- A player whose hand is shown and is to be played from by another player.
- A word serving only to make a construction grammatical.
- An unused parameter or value.
- A feigned pass or kick or play in order to deceive an opponent.
- A bodily gesture meant to fool an opposing player; a feint.
- To make a mock-up or prototype version of something, without some or all off its intended functionality.
- To feint.