Can I use a sub-domain name for a new domain in a new forest ?

Hello, 

I am trying to find some guidance and recommendations for a new domain in a new forest that I have to build.
This new domain will be created on a new platform but a 1-way trust will be created between both domains.
Since the current domain is called mycompany.com, is it possible to call the new domain in a new forestnewdomain.mycompany.com ? What would be a best practice ?

In my opinion, it looks like sub-domain name which is not the case and I don't really want to call the new domain mycompany.local...

How do you think I should call the new domain?

- newdomain.mycompany.com : looks like a sub-domain that would imply a 2-ways trust but I would only have a 1-way trust
- mycompany2.com : I would need to buy another public domain name
- corp.mycompany2.com
- mycompany.local : As far as I know, .local is not recommended practice

Thanks for taking the time to read (I hope it's clear) and for your answers.