catchword (n.)youdaoicibaDictYouDict[catchword 词源字典]
1730, "the first word of the following page inserted at the lower right-hand corner of each page of a book," from catch (v.) + word (n.); extended to "word caught up and repeated" (especially in the political sense) by 1795. The literal sense is extinct; the figurative sense thrives.[catchword etymology, catchword origin, 英语词源]