Should I indicate that definitions are from an article? In my master thesis I included some definitions exactly (just translated in French) like they appear in a paper because they are particularly well written and easy to read for someone who has never dealt with the subject. Of course I do cite the paper, but should I explicitly tell that the definitions are from that paper ?
That is a great question for your advisor. :)

All I can give is my personal opinion on that, and your advisor might have a different opinion (and in the end, he grades your work, not me, so it might be good to find out what he is thinking):
There are two ways to quote a paper. One is to quote its general content, this is marked by something like 


  The following section is based on multiple works by A and B [1,2,5,7].


If, as in your case, you want to directly quote something verbatim, I would make it clear, for example like this


  Definition 7 ([1, theorem 4.3])


Including the exact place where to find it in the original paper helps others to check that you really just quoted verbatim (don't get me started on people who change a quoted theorem to suit their claims...).
As a general rule, always try to make it as easy as possible for people to read and verify your work, without drowning them in unnecessary references. Quoting a famous 50 page research-novel might look good in your sources, but if you don't give the exact place in there, almost no one will have time to check what you are quoting.