The animal threw the missile from the top of a tree after becoming frustrated with his tiring labour, according to reports.Leilit Janchoom, 48, had employed the monkey to pick coconuts which he could then sell for around 4p each.
The animal — named Brother Kwan — found the work tedious and strenuous but Mr Janchoom refused to let him rest, dishing out beatings if he refused to climb trees.
It is believed that the monkey eventually snapped, and targeted his owner from a high branch with one of the hard-skinned fruits.
Mr Janchoom, from the province of Nakorn Sri Thammarat in Thailand, died on the spot after being struck by the coconut, according to reports in a local newspaper.
The dead man’s wife said that the monkey had “seemed lovable” when they bought him for £130.
News of the attacks comes after scientists disclosed this week that a chimpanzee at a Swedish zoo became so annoyed at being gawked at by tourists in a zoo that he started creating weapons to hurl at them.
Santino the chimp would calmly collect stones and fashion discs made out of concrete even when the zoo was closed, to throw at visitors when they returned.
Scientists believe his behaviour is the strongest proof yet that humans are not the only creatures which can make plans for the future.