I have downloaded a spacesim tutorial that uses the following
synonym player_ship {type entity;}
synonym star_sphere {type entity;}

The keyword synonym is not recognized by my version 6.4.
Any help would be appreciated.

Thats a pointer

It is *very* old syntax

synonym player_ship {type entity;}
synonym star_sphere {type entity;}

Should be replaced with:

entity* player_ship;
entity* star_sphere;

EDIT: I do not know the code you downloaded, but I bet that there will be lots of outdated syntax in it... Much has changed since "synonyms" where used

Thanks