ounces

A troy ounce, weighing 1/12 of a troy pound, or 480 grains, or 31.1035 grams.

A US fluid ounce, with a volume of 1/16 of a US pint, 1.8047 cubic inches or 29.5735 millilitres.

A British imperial fluid ounce, with a volume of 1/20 of an imperial pint, 1.7339 cubic inches or 28.4131 millilitres.

A little bit.

Example: He didn't feel even an ounce of regret for his actions.

Now specifically, the snow leopard, Uncia uncia.