In the singular usage it more generally refers to a person holding French citizenship. More specifically, to a Frenchman holding an opinion that is deemed (by the listener) as unsupportive - especially regarding foreign policy or military matters.
It refers to the supposed cultural habits of Frenchmen - cheese eating and surrendering when any slight agressive action is taken towards them or their country. It is considered perjorative in any sense.
No war in Iraq? What are they thinking, those damn Cheese eating surrender monkeys?
the antiquity of this word dates back all the way back...waaay back to the era when the young and tight crustations were forming into the alien robots which took the divinely noun-heavy novels from the future and burned them so that they and their family friends whom kill devoid of compunction can enjoy the fine eats at Maggie's on 42nd.
I hope the bogus futility of M@W ontology will save us from the lava.