expository (adj.)youdaoicibaDictYouDict[expository 词源字典]
1620s, from Medieval Latin expositorius, from exposit-, past participle stem of Latin exponere "set forth" (see expound). Earlier in English as a noun meaning "an expository treatise, commentary" (early 15c.). Related: Expositorial.[expository etymology, expository origin, 英语词源]