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]
demonstration (n.)youdaoicibaDictYouDict
late 14c., "proof that something is true," from Old French demonstration or directly from Latin demonstrationem (nominative demonstratio), noun of action from past participle stem of demonstrare "to point out, indicate, demonstrate," figuratively, "to prove, establish," from de- "entirely" (see de-) + monstrare "to point out, show," from monstrum "divine omen, wonder" (see monster). Meaning "public show of feeling," usually with a mass meeting and a procession, is from 1839. Related: Demonstrational.
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."
monstrous (adj.)youdaoicibaDictYouDict
mid-15c., "unnatural, deviating from the natural order, hideous," from Middle French monstrueux, from Latin monstruosus "strange, unnatural, monstrous," from monstrum (see monster). Meaning "enormous" is from c. 1500; that of "outrageously wrong" is from 1570s. Earlier form monstruous (late 14c., from Old French monstruous) was "very common in the 16th c." [OED].
muster (v.)youdaoicibaDictYouDict
c. 1300, "to display, reveal, appear," from Old French mostrer "appear, show, reveal," also in a military sense (10c., Modern French montrer), from Latin monstrare "to show," from monstrum "omen, sign" (see monster). Meaning "to collect, assemble" is early 15c.; figurative use (of qualities, etc.) is from 1580s. To muster out "gather to be discharged from military service" is 1834, American English. To muster up in the figurative and transferred sense of "gather, summon, marshal" is from 1620s. Related: Mustered; mustering.