@AndyD said:
Showing my age.
Indian, indigenous. Is the word tribes acceptable these days?
First nation? American aboriginals?
Australia I know have gone through this process and is still evolving the non-offensiveness.
Transfer that to the UK and you get a real messy jumble of us mongrel folk 
Personally I like 'aboriginal', even though it is an Italian rooted word.
It’s definitely a bit fraught! Tribe isn’t used here - Nation is a safe term. We use First Nation Métis Inuit as a catch all sometimes but Indigenous has more or less replaced that terminology as well - I think largely because it isn’t acceptable to omit any of those three groups if you are using it as a generic term so it’s a mouthful. Aboriginal was used at one point, especially in legal documents, but it fell out of favour as it was seen as too general. Basically Indigenous leaders have asked that Indigenous be the general term unless you are speaking of a specific Nation or community in which case you should name that Nation. Be specific as possible, and use Indigenous when you are being non specific. When I am talking about a friend of mine with my students I will say that she is an Indigenous person so they understand where I am going with it and then will say that she is an Anishinaabe woman from Bkejwanong. Then I will usually tell them that Bkejwanong is also called Walpole Island, because that is a place name my students will sometimes recognize.
I think of the word “Indian” the same way the one might think of the word “Negro” in the US. While it remains in legal documents and the names of some agencies, it would be offensive to use the term to talk about a person or group of people.