chris collister May 21, 2011:

Technically speaking, there is a very significant difference between a nozzle and a diffuser. The former is intended to increase the speed of the fluid towards the exit, the latter to decrease it. In the context of a fire extinguisher, it would definitely be the latter. If the item concerned flares outwards (as they usually do, at least for gas extinguishers), then it would indeed be a horn or diffuser.

SafeTex May 20, 2011:

Horns and diffusers Nozzle is fine for me but I did find a site where they speak of 'horns' and 'diffusers'.
http://www.flamestop.com.au/shopping/shopdisplayproducts.asp...