What is ecumenism, anyway?

More from the Sin Eater (which just keeps getting better and better, in a mean cynical way):

Poor bewildered 16 year-old Ermyn, who wants to be a believer but, being an Anglican doesn't know how, also doesn't know what Ecumenism is. But she had heard the word somewhere and used it in a pinch when she had to think of something to talk about with the bishop's wife when put on the spot at an awful party.

Later she is again confronted with the dreadful woman:

"Have you thought any more about ecumenism?" Mrs. Flower asked Ermyn.

"Oh yes. Thank you," said Ermyn. "What is ecumenism?" she asked Rose in an undertone.

"It is as though a dying man were to tie himself to one already dead in the hope of setting in train a process of revitalisation," Rose told her, also in an undertone, low but carrying.

"It's lovely," gabbled Peggy parchedig [Welsh; I think it means the vicar's wife]. "Charlie went to talk to the nuns the other day. They were lovely to him. And the Father gave us a sermon at Easter. It was lovely."

"How lovely," said Rose, leaning back on her elbows. "If the progressives in my poor befuddled Church have their way," she said to Ermyn, "thousands more clergymen's wives will be unleashed on to the world. Ponder that, if ever you feel overwhelmed by unreasoning cheerfulness."