I thought the term was 'periphrase', but looking that up it that apparently isn't the case. I don't know how I got my terms mixed up.
By 'words made from a sentence', I mean such words as 'forget-me-not' (name of a flower), and 'hand-me-downs'.
I recall that highly synthetic languages like to do this a lot. But when I tried to look up more information about this, I can't find it because it would seem that I have forgotten the proper terminology.