Be warned that these sorts of discussions are only theoretical .. as when it comes to any specific instance, the answer is always 100% dependent on the specific domains...
There is no correct answer.
Even more important is that while "credit card" can technically be 2 words, it is a single term. So while it's not a single word, it's significantly better than two unrelated words.
(And I'm not even sure if Creditcard specifically is one word or two .. but you know what I mean in general)
Again though .. when looking at deciding between two specific domains .. NEVER use any general guide .. INCLUDING MY OWN .. every domain is unique .. and using some general guideline to decide which is better without taking into account the unique attributes of each specific domain is a good indication that someone quite simply does not understand domains in general.