- frightful or hideous, especially in appearance; extremely ugly.
- shocking or revolting; outrageous: monstrous cruelty.
- extraordinarily great; huge; immense: a monstrous building.
- deviating grotesquely from the natural or normal form or type.
- having the nature or appearance of a fabulous monster.
- extremely; exceedingly; very.
- abnormal, hideous, or unnatural in size, character, etc
- (of plants and animals) abnormal in structure
- outrageous, atrocious, or shockingit is monstrous how badly he is treated
- hugea monstrous fire
- of, relating to, or resembling a monster
adj.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].