Dodoes (found in Africa mainly) were not only big (larger than a swan), but they were barely able to run, and the colonists who settled the islands, along with their pigs, found them delicious. By the early 18th century, gone was the short-winged bird leaving behind only it's sad story and a synonym for something utterly gone or a hopelessly dumb person. Dodo is the corruption of the Portuguese dondo, silly.
Deep Throat:
Dear John,letter:
No one has identified the original jilted John, if there was one, but this term for a letter to a soldier saying that his wife or sweetheart is leaving him for another dates back to World War II. It is often abbreviated to a Dear John and can be used for a similar letter to any man distant from the woman writing it.
Devil's advocate:
Deriving from the Latin Advocatus Diaboli, the "devil's advocate" was first an official appointed by the Roman Catholic Church, his job to argue the case against a person's canonization, or recognition as a holy person. From this the term came to mean anyone who argues against an idea to test it.
desultory:
Circus riders in Ancient Rome jumped from one horse to another during their acts, which led to their being called desultors , or leapers, from the Latin salire , "to leap". They were soon compared to people who fitfully jump from one idea to another in conversation, which resulted in the word desultorious, "to be inconsistent, beside the point,", the ancestor of our English word desultory.
donkey's years:
Means a very long time. The usual explanation for this expression, which is first recorded in 1916, is that donkey's ears is a play on donkey's ears , which are very long indeed.
Domino effect: