FI-Future intended, or more commonly referred to as fiance. As in "My FI and I got in a spat last night because he wanted to wear a powder blue tux to the wedding."
DH-Dear husband. Yes. people actually use this one. Regularly. As in "I love my DH and the 2 carat diamond ring that he bought me for our engagement." (* Insert Subliminal Message Here*)
MIL-Mother-in-law. Everyone has them, no one gets along with them. I don't get it; my FMIL is amazing! As in "My MIL wore white to my wedding and I still haven't forgiven her!"
FSIL,FMIL,FFIL-F can be added to sister-in-law,mother-in-law, father-in-law etc. to denote the future tense. As in, "My FFIL will be walking our puppy down the aisle as our ring bearer."
BM-Could be best man, but usually means bridesmaid. As in "I don't know why the BMs don't love the pink taffeta dresses I chose. The nerve!"
MOH-Maid/Matron of honor. As in "My sister Em will be my MOH."
Knottie-A recently engaged woman who uses the knot (http://www.theknot.com/) for planning/has a knot bio. As in "Knottie soandso had gorgeous centerpieces. You should check them out!"
Ering-Engagement ring. E can also be put in front of any word to denote that it refers to the engagement (i.e. ePics). As in "My eRing is so huge that it hurts my hand to wear it!"