The Collaborative International Dictionary
optically active
optical activity \optical activity\ n. (Chem.) the ability of a chemical compound to rotate the plane of plane-polarized light. This is found only in chemicals whose molecular structure does not have a plane of symmetry, and is common in biochemical compounds. -- optically active adj.
Wiktionary
optically active
a. (context chemistry of a crystal or compound English) Exhibiting optical activity.