river basin and drainage basins the same?

Answer 1

Yes. These terms are synonymous. Both refer to the land region where runoff enters the given river. However, "drainage" basin" can also refer to a lake or ocean, while river basin is more specific. The drainage basin for a large inland sea could include multiple river basins.

Answer 2

Not necessarily.

The term "river basin" is well-defined; it is the land area that supplies surface runoff to a particular river and its tributaries.

The term "drainage basin" is less well-defined; depending on which source you investigate, it could mean the same as river basin or something different.

For instance, a "drainage" basin could be defined as follows:
~ a body of water and the land draining into it. ~
This would include the river, although a "river" basin does not.

See the source link for where this definition came from.

In other cases, "drainage" does not limit itself to rivers. The watershed (land area containing surface water) could drain to a lake or into the ocean directly and still qualify as a drainage basin.