Besides and But

Besides adverb - In addition.

But is a synonym for besides in part of speech topic. In some cases you can use "But" instead the word "Besides" as a preposition or an adverb or a conjunction, when it comes to topics like still, apart from.

But adverb - And nothing more.

Besides is a synonym for but in except topic. You can use "Besides" instead the word "But" as a preposition or an adverb or a conjunction, if it concerns topics such as still, apart from, furthermore.