Supporting, or in accord with, ecumenism(adjective)
A person who espouses ecumenism(noun)
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Use "ecumenist" in a sentence
"That great ecumenist, Cardinal Willebrands, then still at the helm of the Vatican's office for Christian Unity, had written and suggested a deeper ecclesiological study would be most helpful."
"The tensions were evident more than 20 years ago, in a historic exchange of letters among Pope John Paul II, Archbishop Robert Runcie of Canterbury, and Cardinal Johannes Willebrands, the veteran Dutch ecumenist then leading the Vatican's Pontifical Council for Promoting Christian Unity."
"But I feel it has public significance because we have seen a serious decline in the mainline churches in the US over the last half century, a decline I anticipated in the 1960s when I was an ardent ecumenist."