What would you call "razor blade" in Brazilian Portuguese?
suggestions: gilete, lâmina de navalha, lâmina de barbear
If you're asking about the razor used to shave, you can say lâmina or lâmina de barbear. See this picture:
Gillette is often used as a synonym for "razor blade" (at least in Brazil), although it is only a trademark (and not only sells razor blades).
Particularly I would translate for "lâmina" if you are referring only to the piece of metal, which can be part of other tools, like a stylus ("estilete" in portuguese), and "lâmina de barbear" when speaking about razor blade.
It depends on what you use the razor blade for: shaving, lâmina is the term. Like: a package of razor blades. Um pacote de lâminas. The formal term is lâmina de barbear.
navalha is a straight razor with a blade. the blade is also lâmina, but, de navalha.