Etymology
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monstrous (adj.)

mid-15c., "of unnatural formation, deviating from the natural order, hideous," a variant of earlier monstruous (late 14c.), from Old French monstruos, monstrueuse and directly from Late Latin monstruosus "strange, unnatural, monstrous," from Latin monstrum "divine omen, portent, sign; abnormal shape; monster, monstrosity," figuratively "repulsive character, object of dread, awful deed, abomination," from root of monere "to admonish, warn, advise," from PIE *moneie- "to make think of, remind," suffixed (causative) form of root *men- (1) "to think."

Meaning "enormous, huge" is from c. 1500; that of "outrageously wrong, shocking, horrible" is from 1570s. The earlier form monstruous remained "very common in the 16th c." [OED]. As an adverb from c. 1600, but by late 19c. regarded as vulgar or colloquial. Related: Monstrously; monstrousness.

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humongous (adj.)
also humungous, by 1972, American English, apparently a fanciful mash-up of huge and monstrous.
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Fomorian (adj.)
pertaining to the monstrous race in Irish mythology, 1876, from Irish fomor "pirate, monster," from fo "under" + mor "sea." Cognate with Gaelic famhair.
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portentous (adj.)

"of the nature of a portent, ominous," 1540s, from Latin portentosus "monstrous, marvelous, threatening," from portentem "portent," from portendere (see portend). Sometimes portentious, by influence of pretentious. Related: Portentously.

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misshapen (adj.)

"having a bad or ugly shape, crippled, deformed, monstrous," also "degraded, perverted," late 14c., from mis- (1) "badly, wrongly" + old alternative past participle of shape (v.). The verb misshape (1520s) is perhaps a back-formation.

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abraxas 

Cabalistic word associated with the followers of Basilides the Gnostic, by 1680s, of uncertain origin and with many elaborate explanations. Also used in reference to a type of Gnostic amulet featuring a carved gem depicting a monstrous figure and obscure words or words connected to Hebrew or Egyptian religion (1725).

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simurgh (n.)
monstrous bird, rational and ancient, in Persian mythology, 1786, from Persian simurgh, from Pahlavi sin "eagle" + murgh "bird." Compare Avestan saeno merego "eagle," Sanskrit syenah "eagle," Armenian cin "kite." Probably identical with the roc (q.v.).
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roc (n.)

monstrous predatory bird of Arabian mythology, 1570s, from Arabic rukhkh, from Persian rukh. It is mentioned in Marco Polo's account of Madagascar; according to OED, modern use of the word mostly is due to translations of the "Arabian Nights" tales. Hence roc's egg "something marvelous or prodigious." Compare simurgh.

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anamorphosis (n.)

"distorted projection or drawing" (one that looks normal from a particular angle or with a certain mirror), 1727, from Greek anamorphosis "transformation," noun of action from anamorphoein "to transform," from ana "up" (see ana-) + morphosis, from morphe "form," a word of uncertain etymology. In botany, "monstrous development of a part" (1830); in evolutionary biology, "gradual change of form in a species over time" (1852).

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enormous (adj.)
1530s, "abnormal" (usually in a bad sense), from Latin enormis "out of rule, irregular, shapeless; extraordinary, very large," from assimilated form of ex "out of" (see ex-) + norma "rule, norm" (see norm), with English -ous substituted for Latin -is. Meaning "extraordinary in size" is attested from 1540s; original sense of "outrageous" is more clearly preserved in enormity. Earlier was enormyous (mid-15c.) "exceedingly great, monstrous." Related: Enormously; enormousness.
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