Is there a word that describes a pre-wedding party?

Stag Party is often used in the UK to mean either of a Stag party or a Hen party, but generally the two are kept distinct, as they tend to be quite different in the nature of entertainment and activities.

You'll need at least two words here. I think pre-wedding celebration is OK, but could also include a rehearsal dinner, which you're excluding.

I'd suggest last hurrah or if you're in the UK, you could use hag party (which is a combination of hen and stag).