Cheers for the reply, stephankn.

I think the CC attribution licence would apply to the actual geonames rendered mapping - surely place names featured in this ‘work’ would be classed as being in the public domain. Yes, there might be issues with a direct db to db import, but adding names to OSM after manual cross-referencing shouldn’t cause any infringement, should it? You can’t copyright a general populace place name, can you?

Anyways, maybe best to leave the source tag blank then - if you just so happened to be doing a bit of casual reading of geonames prior to editing OSM data… No moral dilemma for me there!