ogive
I think after I looked this one up, I remembered having seen it before. But it's a good word, so: an "ogive" is (among other things) a pointed arch. It's remarkable how many nifty words there are related to cathedral architecture.
I'm not sure y'all will be able to see this, but take a look at MW's arch illustration, featuring an impost, a springer, a voussoir (see also coign), and various kinds of arches. I'm guessing that #3, the lancet arch, is an ogive; however, "ogive" can also be a synonym for "ogee," the kind of onion-dome-profile-shaped arch in #4.
