1. discuss: to talk about something with someone and tell each other "your" ideas and opinions

2. discuss: to talk about something with someone and tell each other "his" ideas and opinions

3. discuss: to talk about something with someone and tell each other "their" ideas and opinions
--------------------------------------------
The definition of 'discuss' is in #1. What about the others? Can't we use 'his' or 'their' instead of 'your'?

"their" is inappropriate. "each (other)" is singular, "their" is plural. Either "your" or "his" is okay. "your" is the same, singular and plural, "his" is singular.

Oh, absolutely! Using "his" or "their" in the definition of "discuss" is completely acceptable. In fact, you can even use "her," "their," or any pronoun that floats your boat! As long as you're talking about something with someone and sharing ideas, feel free to mix it up and have a pronoun party. Just don't forget to bring the snacks!

Yes, in the definitions you provided, the word "discuss" can indeed be used with alternative pronouns such as "his" or "their" instead of "your." This allows for different perspectives and makes the definition more inclusive. So, the word "discuss" can be used in all three ways you mentioned, depending on the context and the pronouns used.

Although the definition you provided for "discuss" primarily uses the pronoun "your" to indicate that two or more people are sharing their ideas and opinions with each other, it can also be used with other pronouns such as "his" or "their" depending on the context.

You can use "his" when referring to a single person talking with someone else and sharing his own ideas and opinions. For example, "He discussed his project with his colleague and received valuable feedback."

You can use "their" when referring to multiple people talking with each other and sharing their collective ideas and opinions. For example, "The team members discussed their strategies before the big game."

The choice of pronoun depends on the subject(s) involved in the conversation. If you are talking about yourself and another person, use "your." If you are talking about a single person, use "his." If you are talking about multiple people, use "their." The pronoun reflects the perspective of the subject(s) involved in the discussion.