The most common and most likely answer to this crossword clue is the 8 letter word MARMOSET
I've seen this crossword clue in The Daily Telegraph
M
A
R
M
O
S
E
T
More clues leading to the result MARMOSET
- Head of menagerie, maestro trained monkey
- Monkey turned over stuff doctor put in place
- Monkey’s limb doctor holds to fix
- Trade centre stocking some knocked-off 24
- Stammer badly describing love for Primate
- Spoil second series of games, being a monkey
- Little monkey hurt doctor with compendium
- Monkey blight fixed after brief time
- Marketplace contains some performing monkey
- Monkey or burrowing animal going round Kent area
Buddy explains!

The straight part
We know that "Monkey" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case monkey = marmoset.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 MARMOSET mean?
MARMOSET noun- A small monkey, now specifically a Central and South American monkey of the genera Callithrix, Mico, Cebuella, or Callibella, with claws instead of nails, and a rather primitive layout.
- A hideous figure; a grotesque.
- An unappealing or foolish man.