Definition of effusion
1
: an act of effusing
2
: unrestrained expression of words or feelings
greeted her with great effusion— Olive H. Prouty
3a(1)
: the escape of a fluid from anatomical vessels by rupture or exudation
(2)
: the flow of a gas through an aperture whose diameter is small as compared with the distance between the molecules of the gas
b
: the fluid that escapes
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Merriam-Webster unabridged
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Time Traveler for effusion
The first known use of effusion was in the 15th century
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