Diploma
mid 17th century (in the sense ‘state paper’): via Latin from Greek diplōma ‘folded paper’, from diploun ‘to fold’, from diplous ‘double’.
wiktionary
From Latin diploma, from Ancient Greek δίπλωμα(díplōma, “folded paper, license”), from διπλόω(diplóō, “I double, fold over”), from διπλόος(diplóos, “double”).
etymonline
diploma (n.)
1640s, "state paper, official document," from Latin diploma (plural diplomata) "a state letter of recommendation," given to persons travelling to the provinces, "a document drawn up by a magistrate," from Greek diploma "licence, chart," originally "paper folded double," from diploun "to double, fold over," from diploos "double" (see diplo-) + -oma, suffix forming neuter nouns and nouns that indicate result of verbal action (see -oma).
The main modern use is a specialized one, "a writing under seal from competent authority conferring some honor or privilege," especially that given by a college conferring a degree or authorizing the practice of a profession (1680s in English).
The plural is always -mas in the ordinary sense (certificate of degree &c.), though -mata lingers in unusual senses (state paper &c.) as an alternative. [Fowler]
Compare diplomacy, diplomatic.
