Monstrous, a.
Etymology: [OE. monstruous, F. monstrueux, fr. L. monstruosus, fr. monstrum. See Monster.]
1. Marvelous; strange. [Obs.]
2. Having the qualities of a monster; deviating greatly from the natural form or character; abnormal; as, a monstrous birth. Locke. He, therefore, that refuses to do good to them whom he is bound to love ... is unnatural and monstrous in his affections. Jer. Taylor.
3. Extraordinary in a way to excite wonder, dislike, apprehension, etc.; -- said of size, appearance, color, sound, etc.; as, a monstrous height; a monstrous ox; a monstrous story.
4. Extraordinary on account of ugliness, viciousness, or wickedness; hateful; horrible; dreadful. So bad a death argues a monstrous life. Shak.
1 more senses
5. Abounding in monsters. [R.] Where thou, perhaps, under the whelming tide Visitest the bottom of the monstrous world. Milton.
1 other Webster entry under this spelling
Monstrous, adv.
Exceedingly; very; very much. "A monstrous thick oil on the top." Bacon. And will be monstrous witty on the poor. Dryden.
Shades of meaning
Fernald has no entry of its own for monstrous; he lists it under absurd.
Where he writes about it:
Monstrous and preposterous refer to what is overwhelmingly absurd; as, "O monstrous! eleven buckram men grown out of two," SHAKESPEARE 1 King Henry IV, act ii, sc. 4. — from absurd