into (prep.)youdaoicibaDictYouDict[into 词源字典]
Old English into, originally in to. The word is a late Old English development to replace the fading dative case inflections that formerly distinguished, for instance, "in the house" from "into the house." To be into something, "be intensely involved in," first recorded 1969 in American English.[into etymology, into origin, 英语词源]