Effusive means showing feeling far more freely than is usual. Thanks, praise or affection, poured out.
The word carries a hint of doubt, since effusive praise is often suspected of being insincere, and British reserve treats any large display of feeling with suspicion. It takes in when a subject is named. The literal root is about pouring out, which is exactly the picture. The adverb effusively usually attaches to thanked or greeted, and the noun effusion means an outpouring, in medicine of fluid and elsewhere of words.
1adjectiveeffusiveExpressing feeling in an unrestrained way.
“He was effusive in his thanks.”
Proto-Indo-European
*ǵʰewd-
Medieval Latin
effūsīvus
English, today
effusive
Medieval Latin effūsīvus, 1660s.
Etymology from Wiktionary, CC BY-SA