DIPTYCHA, in antiquity, a public register, wherein were written the names of the consuls, and other magistrates, among the heathens; and of bishops, and defunct as well as surviving brethren, among the Christians.
The word is formed from the Greek διπτοχον, or διπτοχε, and that from διπτοχ, a masculine noun derived from πτυχω, I fold or plait. From its future πτυχω is formed πτυχ, a fold or plait, to which adding dis, twice, we have διπτοχ, in the genitive διπτοχης, whence the nominative neuter διπτοχον, q. d. a book folded in two leaves; though there were some in three, and others in four or five leaves. An ingenious author imagines this name to have been first given them, to distinguish them from the books that were rolled, called volumina.
It is certain there were profane diptycha in the Greek empire, as well as sacred ones in the Greek church. The former were the matricula, or registers, wherein the names of the magistrates were entered: in which sense diptycha is a term in the Greek chancery.