What is an antonym for the word...?

Well, let's think this through. An informant is one who tells on others. So what is the word for someone who doesn't tell on others? This actually is difficult, because 'informant' is a noun, and no opposite nouns come to mind. However, 'closed-mouth' is an adjective that approximates the opposite of 'informant.'

'Reticent' might also work, but once again, this is an adjective, not a noun.

Antonym Of Reticent

I don't think you will find a noun that means "somebody who doesn't tell on others". But on the basis that an informant is a person who GIVES information, such as a journalist's informant, then an antonym woulld be the word for the person who GETS the information ie receiver, or recipient.

Of course it all depends on the context, which you have not given. I hope this helps a bit.

I guess "traitor" might be one since an informant is someone who gives you information about an enemy and a traitor is someone who gives your enemy information about you...

hope this helps!

I think the opposite of informant is SECRETIVENESS. I hope this is correct.

An enigma.

tight-lipped

patriot

steadfast