marmoset (n.)
"small monkey," late 14c., from Old French marmoset "grotesque figurine; fool, jester" (late 13c.), perhaps a variant of marmote "long-tailed monkey, ape," then, as a term of endearment, "little child;" said to be from marmonner, marmotter "to mutter, mumble," probably of imitative origin. Some French authorities suggest a derivation of marmoset from marmor "marble," as if "little marble figurine."