adjective: bad-tempered; spiteful.
From spleen, from French esplen, from Latin splen, from Greek splen.
Earliest documented use: 1398
In earlier times it was believed that four humors controlled human behavior and an imbalance resulted in disease. According to this thinking an excess of black bile secreted by the spleen resulted in melancholy or ill humor. Also, the spleen was considered to be the seat of emotions. To vent one’s spleen was to vent one’s anger.
Usage (from Wordsmith)
“Kasit Piromya, Thailand’s splenetic foreign minister, has complained that other countries are not helping Thailand to catch a ‘bloody terrorist’.”
Picking Up the Pieces; The Economist (London, UK); May 27, 2010.