compere
Turns out a "compere" is a master of ceremonies (MW11 sez "chiefly British"). And to compere is to emcee.
I had seen "compeer" before (mostly in Pogo, I think), for "companion" or "comrade," and if I had previously encountered the noun "compere" I think I assumed it meant the same thing. I'm pretty sure I hadn't previously seen the verb "compere."
I seem to be posting a lot of British terms here. Which is funny, 'cause I thought I was pretty up on British slang and usage, based on a lifetime of reading British books and watching British TV and being generally an Anglophile. But it turns out they've got all these terms nobody ever told me about. Hmph.
