Adjective. Showing gratitude, pleasure or approval in an unrestrained manner.
... an effusive thank you ...
In geology effusive can also be used to refer to a volcanoe pouring out large volumes of molten rock. The effusive volcanoe shares the trait of gushing with those offering such heartfelt platitudes.
The use of the word peaked in the late 19th century, possibly coinciding with the eruption of Krakatoa when 70% of the island collapsed generating a shockwave which traveled around the world three times.