Pentaerythrityl refers to the alcohol (pentaerythritol, also called pentaerythritol) which is esterified with the fatty acid stearic acid (octadecanoic acid). The prefix "penta" refers to the 5 carbon atoms of the molecule. Pentaerythrityl stearate is used in cosmetic formulations. The ester mixture acts as an emollient (makes the skin smooth and supple).