But now he has come to

Question

In the Orient Long Man's dictionary Word Master I have found the different uses of ' to' - as a preposition, to infinitive and an adverb

The example is given for its use as an adverb

He was unconscious for some time, but now he has come to = return to a conscious state.

Native speakers can understand its meaning but non native speakers of English can not understand What "come to" means

What is "come to " here? Is it an idiom or something else?

I would like to know how "to" can be used as an adverb in different contexts?

Answer 1

"Come to" is a phrasal verb which means "to become conscious again after an injury or medical operation".

come to

phrasal verb with come ​

to become conscious again after an accident or operation:

Has he come to yet?

Come to (Cambridge Dictionary)

In English, a phrasal verb is a phrase such as turn down or ran into which combines two or three words from different grammatical categories: a verb and a particle and/or a preposition together form a single semantic unit. This semantic unit cannot be understood based upon the meanings of the individual parts, but must be taken as a whole.

Phrasal verb (Wikipedia)