1. An instance of giving off an odor or smell: There was an intensely malodorous effusion coming from under the porch at the back of Sara's house that was from a skunk because it was defending itself from the threats of her dog which was barking at it.
2. In medicine, an escape of fluid into a body cavity: The surgeon installed a thin tube into the incision of the abdomen of the patient which would control the effusion, allowing it to drain out of the body and not contribute to possible infections.
3. An instance of unrestrained speech or writing: Although initially very controlled, the convocation speaker eventually spoke with great effusion about the future that lay before the graduate students.