The most common and most likely answer to this crossword clue is the 6 letter word DONKEY
I've seen this crossword clue in The Guardian
D
O
N
K
E
Y
More clues leading to the result DONKEY
- An age that's critical during dry season abroad
- Idiot's guide provided by university lecturer
- Foreign gentleman leading an ass
- Beast of burden put on small island
- Fellow with vital dope
- Stupid person put on island
- Head of Mafia meeting important smuggler
- Silly fool is to slip on island
- Teacher essential for this dimwit
- Teacher vital for stupid person
Buddy explains!

The straight part
We know that "dimwit" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case dimwit = donkey.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 DONKEY mean?
DONKEY noun- A domestic animal, Equus asinus asinus, similar to a horse
- A stubborn person
- A fool
- A small auxiliary engine
- A bad poker player