The community pronounces it YOU - NID most of the time; however if you talk to anyone from Lotus/Westford/Product Dev, they all pronounce it UN-ID, like the beginning of "under" and "id" like Id and Ego - so UN-id.
Just like ACL when referring to Notes/Domino is called "ACK-LE", but when talking about your knee it's "AY-CEE-EL"
And of course, my favorite:
the little triangle thingy in the upper right of a database "chicklet" (another "official" word!) - IOW the big db icon - on the workspace, where you change the replica, is called the "hinky minky". Mussie Shore named it this many, many, many years ago. In fact it is still referred to as Hinky Minky in quite a lot of the documentation. :)