thanks Russ.
remembering the contact's name is not the problem, i just seek a way to
address  a letter to someone more intuitively (e.g. when i think of my dad i
don't think of his name but of the word "Dad", same with girlfriend or
whatever).
The workaround suggested by Sue solves that but maybe MS should consider a
more straightforward way to do that (assuming I'm not the only one calling
for it...).

This might seem a picky matter, but I find those little things meaningful
for the more sophisticated users.

btw i found that the autocompletion feature can be misleading in a situation
where you have a contact name that called "abc" and an autocomlete entry
(that's in your contacts) that starts with "abcde".
Writing "abc" and pressing Tab will choose the autocomplete person when I
guess the contact should be preferred and not someone you once sent a letter
to, since after all you did write its exact name... (or at least give you a
chance to choose). And deleting "abcde" is not such a simple task (yes, i
stood on it and pressed "Delete" but it kept coming back!).
anyway... that's a different story altogether ;)