introductory (adj.)youdaoicibaDictYouDict[introductory 词源字典]
c. 1600, from Late Latin introductorius, from introduct-, past participle stem of introducere "to lead in, bring in" (see introduction). Also used in English from c. 1400 as a noun meaning "introductory treatise or textbook."[introductory etymology, introductory origin, 英语词源]