monsteryoudaoicibaDictYouDict[monster 词源字典]
monster: [13] Monster originated as a word for a ‘divine omen or warning’. It goes back via Old French monstre to Latin mōnstrum, a derivative of the verb monēre ‘warn’. From its original sense ‘warning of misfortune, evil omen’, mōnstrum was transferred to the sort of thing that could function as such an omen – a ‘prodigy’, or a ‘misshapen or horrifying creature’ – whence the meaning of English monster.

The word’s connotations of ‘largeness’ seem to be rather more recent, first emerging in English in the 16th century. Other English derivatives of mōnstrum, some of them reflecting a later sense of monēre, ‘show, inform’, rather than the original ‘warn’, include demonstrate [16], monstrance [16], muster [13] (which originally meant ‘display’), and remonstrate [16].

And from monēre itself come admonish, monitor [16], monument [13], premonition [16], and summon [13].
=> admonish, demonstrate, monitor, monument, muster, premonition, remonstrate, summon[monster etymology, monster origin, 英语词源]
horrify (v.)youdaoicibaDictYouDict
1791 (implied in horrifying), from horror + -fy. Related: Horrified; horrifying.