"belonging to or serving as a preface, introductory," 1670s, from Latin praefat-, past-participle stem of praefari "to say beforehand" (see preface (n.)) + -ory. Related: Prefatorial; prefatorily.
Entries linking to prefatory
preface n.
late 14c., "an introduction to the canon of the Mass," also "statement or statements introducing a discourse, book, or other composition; series of preliminary remarks, written or spoken," from Old French preface "opening part of sung devotions" (14c.) and directly from Medieval Latin prefatia, from Latin praefationem (nominative praefatio) "fore-speaking, introduction," in Medieval Latin "prologue," noun of action from past participle stem of praefari "to say beforehand," from prae "before" (see pre-) + fari "speak," from PIE root *bha- (2) "to speak, tell, say."
-ory
adjective and noun suffix, "having to do with, characterized by, tending to, place for," from Middle English -orie, from Old North French -ory, -orie (Old French -oir, -oire), from Latin -orius, -oria, -orium.
Latin adjectives in -orius, according to "An Etymological Dictionary of the French Language," tended to "indicate a quality proper to the action accomplished by the agent; as oratorius from orator; laudatorius from laudator. The neuter of these adjectives was early employed as a substantive, and usually denoted the place of residence of the agent or the instrument that he uses; as praetorium from praetor; dormitorium from dormitor; auditorium, dolatorium.
"These newer words, already frequent under the Empire, became exceedingly numerous at a later time, especially in ecclesiastical and scholastic Latin; as purgatorium, refectorium, laboratorium, observatorium, &c." [transl. G.W. Kitchin, Oxford, 1878]