How to retrieve the name of a lookup field in c#?

If I have a lookup to another entity, let's say contact and account, how do I retrieve the name of that field through c#?
The way I do it in javascript with the web api is : /RelationshipDefinitions/Microsoft.Dynamics.CRM.OneToManyRelationshipMetadata?$select=ReferencingAttribute,ReferencingEntity&$filter=ReferencedEntity%20eq%20%27account%27%20and ReferencingEntity eq 'contact' 
I'm not even sure if that is the best way in javascript either.. I can't seem to find this information anywhere