To occlude is “to close, shut, or stop up”. Simple word, simple meaning – and yet I’ve never run across it before! Maybe my mind was occluded by other thoughts, so I just never remember seeing it. I do have a tendency to just skip over the words I don’t know, because I’m too lazy to look them up. But don’t tell anyone that!
Anyway, occlude comes from Latin occludere, a combination of ob “against, up” and claudere “to shut, close”, according to the OED (the Online Etymology Dictionary, not the Oxford English Dictionary).
Occluding or occlusion, the act of occluding, has a number of specific meanings in different fields. In phonetics, for example, it’s a “momentary complete closure at some area in the vocal tract, causing stoppage of the flow of air and accumulation of pressure.” A coronary occlusion is the “closure or blockage of a blood vessel”, and an occluded front is when a cold weather front covers a warm front (or something like that – I’m not a meteorologist).