late 12c., "professional interpreter of the Jewish Law" (late 11c. as a surname), from Church Latin scriba "teacher of Jewish law," used in Vulgate to render Greek grammateus (corresponding to Hebrew sopher "writer, scholar"). It is a special use of Latin scriba "keeper of accounts, secretary, writer," an agent noun from the past-participle stem of scribere "to write" (from PIE root *skribh- "to cut").
The sense "one who writes, official or public writer" in English is from late 14c. That of "copyist, transcriber of manuscripts" is from 1530s. Used loosely for "an author, one fond of writing" by 1580s.