noun
- a length or portion of time.
- a distinct portion of time with particular characteristics.
- a major division of geological time, forming part of an era.
- a lesson in a school.
- (also menstrual period) a monthly flow of blood and other material from the lining of the uterus, occurring in women of child-bearing age when not pregnant.
- chiefly N. Amer. a full stop.
- Physics the interval of time between recurrences of a phenomenon