a legendary animal combining features of animal and human form or having the forms of various animals in combination, as a centaur, griffin, or sphinx.

any creature so ugly or monstrous as to frighten people.

any animal or human grotesquely deviating from the normal shape, behavior, or character.

a person who excites horror by wickedness, cruelty, etc.

any animal or thing huge in size.

Biology .

an animal or plant of abnormal form or structure, as from marked malformation or the absence of certain parts or organs.

a grossly anomalous fetus or infant, esp. one that is not viable.

anything unnatural or monstrous.

huge; enormous; monstrous

a monster tree.

noun

abnormality , barbarian , beast , behemoth , brute , centaur , colossus , demon , devil , dragon , fiend , frankenstein , freak , giant , hellion , horror , leviathan , lusus naturae , mammoth , miscreation , monstrosity , mutant , ogre , phoenix , savage , titan , villain , werewolf , whale , goliath , jumbo , archfiend , ghoul , tiger , vampire , afreet , bogeyman , bogie , bucentaur , cerberus , chimera , creature , cyclops , enormity , gargoyle , gigantes , gila , gorgon , harpy , hippocampus , huge , hydra , kraken , lamia , medusa , minotaur , monstrosity lususnatur , naiad , nereid , orc , prodigy , scoundrel , scylla , sphinx , yeti , zombie

adjective

behemoth , brobdingnagian , bunyanesque , colossal , cyclopean , elephantine , enormous , gargantuan , gigantesque , gigantic , herculean , heroic , huge , immense , jumbo , mammoth , massive , massy , mastodonic , mighty , monstrous , monumental , mountainous , prodigious , pythonic , stupendous , titanic , tremendous , vast