the interval of time between successive occurrences of the same state in an oscillatory or cyclic phenomenon, such as a mechanical vibration, an alternating current, a variable star, or an electromagnetic wave
a flow of blood and other material from the lining of the uterus, occurring in non-pregnant women at intervals of about 28 days between puberty and the menopause and typically lasting for a few days
she's got her period
period pains
a set of elements occupying a horizontal row in the periodic table
a complex sentence, especially one consisting of several clauses, constructed as part of a formal speech or oration