The most common and most likely answer to this crossword clue is the 9 letter word BIRDBRAIN
B
I
R
D
B
R
A
I
N
More clues leading to the result BIRDBRAIN
- Clever chap supporting Turkey? Or a fool?
- Martin possibly confused Brian, the fool
- Underwear for the tits? Popular for ass!
- Genius? No time to come to our country without it!
- Fool swinging both ways on road? Refuse to go round one
- Swift, say, support at home for idiot
- . One below par mostly without support, name's Charlie
- Clever person after time becomes idiot
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 = birdbrain.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 BIRDBRAIN mean?
BIRDBRAIN noun- Someone who is not intelligent.