/i fyooh"zheuhn/ , 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.
[ 1350-1400; ME ( effusion- (s. of effusio ), equiv. to ef- EF- + fusion- FUSION ]