diplomayoudaoicibaDictYouDict[diploma 词源字典]
diploma: [17] Etymologically, a diploma is a ‘folded paper’. It comes via Latin diplōma from Greek díplōma; this was a derivative of the verb diploun ‘fold’, which in turn came from diplous ‘double’ (a distant cousin of English double). Since official letters tended to be folded over, díplōma eventually came to mean ‘document, especially one issued by the government’ – the sense in which the word was acquired by English.

In the 17th and 18th centuries, the use of the derived Latin adjective diplōmaticus ‘relating to official documents’ with specific reference to the field of international relations led eventually to its French descendant, diplomatique, coming to mean ‘relating to international relations’. English acquired the word as diplomatic in the 18th century.
=> double[diploma etymology, diploma origin, 英语词源]
diploma (n.)youdaoicibaDictYouDict
1640s, "state paper, official document," from Latin diploma, from Greek diploma "license, chart," originally "paper folded double," from diploun "to double, fold over," from diploos "double" (see diploid) + -oma. Specific academic sense is 1680s in English.