Three is a key feminine number, linked to the nutritive force (Mama); the Yoni (Vulva); its abstraction as a Downward Triangle; to the 3 Phases of the Moon; the Triple Goddess ( 3 Goddessss; 3 Graces, 3 Fates, 3 theological Virtues; 9 Muses); the 3 Ages of Woman (cf. 3 Ages of Man). It becomes the starting point for a number of female symbols: the Tricaria (symbol of Demeter and later of Sicily); the trisle, triskell.
It becomes one of the first ordering principles: the 3 Worlds; the 3 columns, 3 pillars. 3 becomes an important male symbol through the Trinity and the starting point for 3 Gods.
In Geometry, the triangle is the first enclosed form. It contians 180 degrees.
In Astronomy, 3 is linked with the Summer Triangle and the Bethelem Triangle.
In India 3 is connected to fire (Vahni) while 4 is connected to water.
tri- as in: