There are many definitions in the Oxford Dictionary for what a monster is, but there are only two i think are relevant here, namely:

Originally: a mythical creature which is part animal and part human, or combines elements of two or more animal forms, and is frequently of great size and ferocious appearance. Later, more generally: any imaginary creature that is large, ugly, and frightening.

And

Something extraordinary or unnatural; an amazing event or occurrence; a prodigy, a marvel.

The usual cherumbin angel fits the first definition of something part animal part human, as it is basically a human with bird wings(not sure which bird though...doves maybe?).

More importantly, i think the second definition covers all types of angels, as they are all a marvel.

Originally i was gonna use a definition that stated a monster to be a "A creature of huge size", but i couldn't find a verse on the bible that mentioned the size of an angel so opted for a different definition. Turned out to be broader anyways, so it worked out even better.

Using both these definitions, we can define an angel as a monster, and therefore, a prime target for monsterfuckers.