What's the exact meaning of とする in this sentence?

Question

I'm trying to understand the construction もうろうとしてる in this line from Mob Psycho 100 Episode 12:

もうろうとしてるようだけど。

It's translated as "he looks like he's about to pass out"。

I found a usage of もうろうとする on eow.alc.co.jp which matches the meaning "to zone out", but I'd like to understand how to deconstruct this form, if that's possible. (for example, my dictionary doesn't know the above construction, so I imagine it's a compound of some kind).

I thought this might be とする, meaning "to be about to ...", as that matches the translation, but according to jisho, that form must follow the volitional form of a verb, whereas here, it follows a と-adverb (or たる-adjective, depending how you look at it).

I've also found 必要とする in the wild which seems like a similar construct, but here 必要 is just a regular noun (and that word actually appears in the dictionary too).

Does anyone know if there is some rule that could explain this construct?

Answer 1

Did you see definition #8 in the Jisho link you posted to とする? I think that should clear things up for you:

to feel (e.g. after sound symbolism or psychological experience word); to look; to feel like​

もうろう is clearly a psychological experience meaning hazy/"out of it", so もうろうとする can be translated as "to feel/act hazy".

The "about to pass out" part they provided is a freedom of translation. The actual Japanese sentence doesn't explicitly say anything about passing out.

Answer 2

From my Japanese grammar book, "Oxford Japanese Grammar & Verbs": "Japanese has many words which imitate sounds, or describe the way something is done, or describe psychological states or feelings by their sound." Many of these words can be used as adverbs when used with the "to" particle.　So もうろう belongs to a special class of onomatopoetic words.

This is confirmed by jisho.org's definiton of "もうろう" which describes it as an "adverb taking the 'to' particle"。

For example,

犬がワンワンと鳴いていた。 inu ga wanwan to naite-ita. The dog was barking.

So the sentence "もうろうとしてるようだけど。" suggests that the speaker wants him to do something but from the way he's been behaving (shite-iru-you-[ni]) suggests that he is going to pass out (mourou) instead (dakedo).