prolegomenon (n.)

1650s, "learned preamble to a book," from Greek prolegomenon, noun use of neuter passive present participle of prolegein "to say beforehand," from pro "before" (see pro-) + legein "to speak" (from PIE root *leg- (1) "to collect, gather," with derivatives meaning "to speak (to 'pick out words')") + suffix -menos (as in alumnus). The same sense is in preface (n.). Related: Prolegomenary; prolegomenous.