Pronunciation: (i-fyOO'zhun),[key] —n. 1. the act of effusing or pouring forth.
2. something that is effused.
3. an unrestrained expression, as of feelings: poetic effusions. 4. Pathol. a. the escape of a fluid from its natural vessels into a body cavity.
b. the fluid that escapes.
5. Physics.the flow of a gas through a small orifice at such density that the mean distance between the molecules is large compared with the diameter of the orifice.