What part of speech is the word coming in following sentence he saw multitude to him?

The word "coming" is not present in the sentence "He saw multitude to him." Therefore, we can't determine its part of speech in this context.

It seems like the sentence might be missing a word or two. If we add the word "coming," we get:

He saw the multitude coming to him.

In this case, "coming" is a present participle acting as an adjective modifying "multitude".