Hello Gabriel,

> Does anybody could help me with the definition of each of the Pali terms
> "Citta, manas, e vinana".

You can find some helpful information in the threads:

http://www.lioncity.net/buddhism/index.php?showtopic=22507
http://www.lioncity.net/buddhism/index.php?showtopic=18449
http://www.lioncity.net/buddhism/index.php?showtopic=23220

> In the abhidhama is stated that they are equivalent.
>
> But if they are synonymous why Lord Buddha made usage of 3 different words?

Abhidhamma and Sutta usages of the terms markedly differ.

Best wishes, Dmytro