Real Dictionary

premenstrual syndrome
uncountable noun: Premenstrual syndrome is used to refer to the problems, including strain and tiredness, that many women experience before menstruation. The abbreviation PMS is often used.

premenstrual syndrome in American English
a group of physical and emotional symptoms that may precede a menstrual period, as fluid retention, fatigue, depression, irritability, etc.
noun: a complex of physical and emotional changes, including depression, irritability, appetite changes, bloating and water retention, breast soreness, and changes in muscular coordination, one or more of which may be experienced in the several days before the

premenstrual syndrome in British English
noun: a group of symptoms, including nervous tension and fluid retention, any of which may be experienced as a result of hormonal changes in the days before a menstrual period starts