Wiktionary
octamethylcyclotetrasiloxane
n. (context chemistry English) A particular cyclic siloxane.
Wikipedia
Octamethylcyclotetrasiloxane
Octamethylcyclotetrasiloxane, also called D, is an organosilicon compound with the formula [(CH)SiO]. lt is a colorless viscous liquid. It is a common cyclomethicone. Like other cyclomethicones, it is slightly volatile. It has attracted scrutiny because it is pervasive in the environment.