Definition of Atheism

[SkepticismFirst]

Atheists could also say that they reject God because there are good intellectual reasons to believe that God doesn't exist. Why not just say that instead?

This is about the definition of the word atheism - Dicitonary definition

Disbelief or lack of belief in the existence of God or gods.

That's all that's needed for a definition.

I lack belief in deities being objective realities even though there's plenty of evidence that people can have subjective experiences which they interpret as being a deity. My personal opinion would be stated in a discussion, though, because it's not the dictionary definition.

You're missing the point. Instead of arguing over definitions, you could be defending a proposition. Why not do that instead? It'll force the theists you talk to into a difficult position where they'll have to try to rebut strong arguments. Simply repeating "I lack belief!" at them ad nauseum accomplishes nothing.