If a songwriter is not the "official" author of a song (I mean his name is not given as the author of it) but he has anyway, let's say unofficially taken part in the musical composition. Is it ok to say:
The song was written by W and Y. But the news that G. had taken part in the compositio/ had collaborated in/with the musical composition was soon widespread
Collaborate implies that it was a rather interactive process. If he wrote one paragraph of the lyrics and sent it to W and Y, then he contributed to it. If W and Y sat with G and together they worked it out, then he collaborated.
Note that "to the composition of the lyrics" means the words. If he was reponsible for the tune, but not the words, then don't use that phrase.
thanks. Since I don't know whether the tune or the lyrics can I say: He contributed to (or collaborated to) the composition?
How about the simple "to the song"?