What's the logic behind adjectives constructed with a hyphen?

Question

I'll give you a lovecraftian stanza:

Thro’ the ghoul-guarded gateways of slumber,
Past the wan-moon’d abysses of night,
I have liv’d o’er my lives without number,
I have sounded all things with my sight;
And I struggle and shriek ere the daybreak, being driven to madness with fright.

Nemesis — Howard Phillips Lovecraft

Ghoul is a noun, and guarded is the past participle of to guard. He combined both words to create an adjective to describe his "gateways of slumber" properly.

But then you have wan-mooned. An adjective plus the past participle of to moon or some bizarre usage of the noun moon to explicitly say that the "abysses of night are full with moons."

That's where I think: What's the logic behind this after all? To which extent I have the power of freedom to create my own bizarre adjectives by combining random words?

I could replace the second verse with:

Past the wild-river’d clouds of mars

It would not make any sense, but the logic of wild-river'd is pretty much the same of wan-moon'd.

What's the insanity-guarded logic/rule behind this?

Answer 1

Wan-moon'd is a perfectly ordinary English construction, in which ADJ-NOUNed is a compound adjective mean “exhibiting or marked by or provided with (an) ADJ NOUN”. For instance:

red-faced with exertion
brown-shirted minions
a one-legged man
horny-handed sons of toil
pluck bright honour from the pale-faced moon

Lovecraft's abysses of night are overlooked or (as Peter Shor suggests) lit (however inadequately) by a wan moon.

Answer 2

Hyphens come in handy especially in examples like yours, where an adjective is used to describe another adjective, thereby acting as an adverb. The hyphen lets us know that the descriptor is acting like an adverb modifying the adjective, not as an adjective modifying the noun.

Is it an abyss that it both wan and moon'd? Or is it an abyss that is wan-moon'd? The hyphen answers that question. There are many more practical instances than in Lovecraftian verse, too.