What are synonyms for besides?

Answer 1

Depends on the context.

If you are using to show position (e.g. the chair is beside my bed) then you can use: next to, alongside or adjacent to. If you are using it to compare (e.g. she looked ugly beside her sister) then you can use: compared to or in contrast with. Lastly, if you are using the word as a preposition (e.g. I love all vegetables, besides spinach) then you can use: apart from, except, excepting, excluding

Answer 2

apart from, barring, excepting, other than, excluding, as well as, in addition to, also, further, otherwise, moreover, furthermore