[tdwg-content] synonyms in DwC Archives

I'm looking for recommendations on how best to put synonyms for taxon records into DwC Archive format.

I'm assuming that these would go into an extension file. Do I have this right? What I'm having more trouble with is determining the right column term. there's dwc:vernacularName, which is also in the examples, but what about synonyms of different types that come with taxonomies (such as NCBI's) or that result from merging taxonomies. There isn't an obvious candidate in DwC, and the list at http://rs.gbif.org/core/dwc_taxon.xmldoesn%27t have a suggestion either that would seem pertinent.

Any suggestions, pointers to documentation or examples?

-hilmar