c.1600, "a dictionary," from Mod.L., from Gk. lexikon (biblion)
"word (book)," from neut. of lexikos
"pertaining to words," from lexis
"word," from legein
"say" (see lecture
). Used originally of dictionaries of Gk., Syriac, Hebrew and Arabic, since these usually were in Latin and in Mod.L. lexicon,
, was the preferred word. The modern sense of "vocabulary proper to some sphere of activity" (1640s) is a figurative extension.