Card, definitely.
Card = it IS the entity.
Cartridge = case that CONTAINS the entity
Hmm,but wait....what then is an "empty cartridge case". An empty case that does not contain a cartridge (so the non-contained entity is the cartridge), or a cartridge case that is empty (so the case is the cartridge, therefore the non-contained entity is NOT the cartridge)?
Still...credit card, playing card, game card. None of them protected by, held in place by, enclosed by, a case. No case = no cartridge, therefore:
Still going with "card"
Charlie
(if only all of life's questions were this hard!)