marmoset

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Any of various very small New World monkeys of the genera Callithrix and Cebuella, having a long tail and long incisors that they use to penetrate bark to extract gum and sap.

from The Century Dictionary.

• noun A little ape or monkey.
• noun Now, specifically, a small squirrel-like South American monkey of the family Hapalidæ, or Mididæ (which see for technical characters).
• noun An ugly little fellow; a conceited “puppy.”

from the GNU version of the Collaborative International Dictionary of English.

• noun (Zoöl.) Any one of numerous species of small South American monkeys of the genera Hapale and Midas, family Hapalidæ. They have long soft fur, and a hairy, nonprehensile tail. They are often kept as pets. Called also squirrel monkey.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun small soft-furred South American and Central American monkey with claws instead of nails