Right now we have both tags, they're separate but contain the same sort of pictures. The cross tag currently has more entries and for good reason, it's the more proper term. If you look up crucifix its general description is the cross with a body (normally Jesus Christ) pinned to it. A cross is just a cross.

The tag right now is being poorly used, but I'd rather it not be aliased to cross. There aren't too many images under crucifix so I think it'd just be fine to clean it up.

I proposed the same thing but as an implication a long while back, but it was never accepted. I still think it might be useful to have an implication, at least.

I'd personally use crucifix for a pendant and cross for an actual cross.

I've only ever heard the definition that it is the cross with the body of Jesus on it. The Merriam-Webster dictionary only carries that definition, and the American Dictionary defines it as either that or "a cross viewed as a symbol of Jesus's crucifixion." Wikipedia defines it as a cross with Jesus' body on it saying it's "from Latin cruci fixus meaning '(one) fixed to a cross.'"

The majority of cross tagged images seem to be typically small pendent like crosses already, at least from what I've seen through glimpsing around in it.