Tim, your spelling is perfectly good for writing it in English.
It being a French word, I use the diacritical character: Alt + 0232 gives me the needed
accent grave to write it as
cerveillière. Freely translated, the word means "brain thingy," and has nothing whatever to do with surveillance.
But seriously, SCAdians could use such a piece as fight-marshal's gear. These men are the closest to the action, excepting the fighters, and it's a good idea for these men to use head protection. They have to have their vision and hearing completely unobstructed if at all possible, to fulfill their function as safety officers, so an enclosed helmet or helm is not preferred for this job.
What you usually see for hardening SCA marshals' heads is something of the kettlehat persuasion -- usually a soup-plate helmet, and one that probably once was painted white and had a CD decal on its front, left over from WW2.