Small monkey (8)
I believe the answer is:
marmoset
'small monkey' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for marmoset that I've seen before include "Small tropical American monkey" , "Monkey with claws" , "Take me to arms about bushy-tailed monkey of tropical America" , "Somme rat? (anag)" , "Small monkey - Rome's mat (anag)" .)