According to Freeman  the word 'protocol' comes from the Greek proto (first) and kolla (glue) and indicated the first sheet of a roll of papyrus whose sheets are glued together. It "listed the contents of the manuscript and its purport." The American Heritage Dictionary  concurs. The reason this caught my attention is that in most network protocols the first part of a packet is generally the header, which also lists its contents.
 Morton S. Freeman, The Story Behind the Word, ISI Press, Philadelphia, 1985, pp. 218-219.
 The American Heritage Dictionary of the English Language, fourth edition, Houghton Mifflin Company, New York, 2006, p. 1410.