I haven’t read anything else by Hurston so have no idea what to make of her coinage –if it is a coinage — of “monstropolous” in Their Eyes Were Watching God, and neither is the internet being forthcoming about it. Here are the two passages in which the word occurs:
[7] “Time makes everything old so the kissing, young darkness became a monstropolous old thing while Janie talked.” (This is just before Janie tells Phoebe her story.)
[161] “Ten feet higher and as far as they could the muttering wall advanced before the braced-up waters like a road crusher on a cosmic scale. The monstropolous beast had left its bed. The two hundred miles an hour wind had loosed its chains.” (This is just before they leave their cabin in flight from the hurricane and seems to refer to Lake Okeechobee.)
One effect of its use is to invite a comparison of these passages and of the two things it is used to describe in these passages: the darkness as Janie unveils her story, the lake that’s been riled by the hurricane.
.i`` * ^ / . . . . . ` `~ 