Should we use the word 'metaphor' in talking about the cross?

Yes, I think so. We should use the word 'metaphor' (although I am happy with 'models' or 'analogies' I guess - see JI Packer) because:

1 - 'descriptions' as a term simply does not tell us what is going in in the relationship between the words and their meaning.

2 - 'metaphor' reminds us that the language being used is being stretched beyond its ordinary sphere of reference, and so we need to be careful in how we use it. If we fail to see that the langauge is metaphorical in nature, we distort it badly.

3 - metaphors are a not to be afeard of. They can be a precise way communicating actual, real things. In fact, they are ideally suited to expressing things that are new or singular in human experience. Like the atonement.

4 - that the langauge of the NT re the atonement is metaphorical allows us to see how the different metaphors moderate and shape one another - especially when we see Paul stringing his metaphors together, as in Rom 3:21-31. If we just say these are 'descriptions', then we are not likely to be as aware of how this goes on in the Scriptural texts.

The 'ransom' example shows how everything can go badly wrong if we don't reckon with the metaphorical nature of the language we are using. Jesus' death IS ransom-ish - it can be understood as resembling that interaction between human beings that we name 'ransom', but if we press the metaphor too far (which the Bible doesn't do) we start making theologically dangerous statements about the devil being paid a ransom price and so on.

Now what about sacrifice?

Nothing on the surface about Jesus' death was sacrificial, in the usual sense of the word. He did not apparently die 'for' anyone, in the sense that a lifesaver might die trying to save a drowning person. It just looked like an ordinary execution. There was no religious ritual. It happened outside the temple, not in it. There was not an offering priest. There was a human and not an animal victim (expressly forbidden in the OT). It is very different to a sacrifice as the Jews (and the pagans) knew it. Right?

So when we hear Jesus himself and the other NT writers refering to Jesus' death as a sacrifice, we know that some stretching and rennovating of the concept of sacrifice is going on. And so it proves: Jesus's death on the cross is yoked to the notion of sacrifice familiar to Israel from its history and from its religious life; and it is done in such a remarkable way that the very notion of sacrifice itself is completely transformed! Hebrews has to show how Jesus is both priest AND sacrifice in order to make it work. In what previously known sacrificial system was this the case? Jesus calls his body 'the temple' (it's a metaphor again!) in order to indicate that now serves the function of and discplaces the original temple.

This is part of our difficulty here: the yoking of the idea of 'sacrifice' to Jesus' death has so transformed our human thinking about sacrifice (at least in the Judaeo-Christian west) that we find it hard to imagine a way of thinking about sacrifice without Jesus' death. (see Nick Colyer's comment)

Further, we feel uneasy with the term 'metaphor' because we want to know (rightly) that the Biblical langauge is a) not random and b) describes actual things that occurred between us and God and not just pictures of the possibility of something occurring. But furrow not your brows: a) the metaphors are NOT random, but revealed and inspired and b) they do depict real and actual things that occurred.

Was the death of Jesus a sacrifice, actually? Well, yes: but not like one that has ever been made before or since. By calling it a sacrifice the NT writers have helped us to relearn what sacrifice actually means all over again!