A minster is a large, important church, especially in England. Long ago many of these churches belonged to a monastery — a house where monks lived and prayed — and the word still carries that old weight. York Minster is a famous one; Westminster means the minster that stood to the west of old London. Though actually, a minster is not automatically a cathedral. A cathedral is the church of a bishop. Some minsters, like York Minster, are cathedrals too, but the two words are not the same job. In everyday talk you mostly meet minster inside place names rather than as a free word for any big church. It sounds like minister (a priest, or a government officer), but that is a different word with a different story.