any South American marmoset of the genera Saguinus and Leontopithecus (Leontideus), having silky fur and a nonprehensile tail: several species are threatened or endangered.
tam·a·rin (tām'ə-rĭn, -rān') n. Any of various small, long-tailed, arboreal monkeys of the genera Leontideus and Saguinus of Central and South America, closely related to and resembling the marmosets but having a larger body, longer limbs, and lower canines that extend well beyond the incisors.