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]
monster (n.)youdaoicibaDictYouDict
early 14c., "malformed animal or human, creature afflicted with a birth defect," from Old French monstre, mostre "monster, monstrosity" (12c.), and directly from Latin monstrum "divine omen, portent, sign; abnormal shape; monster, monstrosity," figuratively "repulsive character, object of dread, awful deed, abomination," from root of monere "warn" (see monitor (n.)). Abnormal or prodigious animals were regarded as signs or omens of impending evil. Extended by late 14c. to imaginary animals composed of parts of creatures (centaur, griffin, etc.). Meaning "animal of vast size" is from 1520s; sense of "person of inhuman cruelty or wickedness" is from 1550s. As an adjective, "of extraordinary size," from 1837. In Old English, the monster Grendel was an aglæca, a word related to aglæc "calamity, terror, distress, oppression."