ecumenism n.

late 16c., "representing the entire (Christian) world," formed in English as an ecclesiastical word, from Late Latin oecumenicus "general, universal," from Greek oikoumenikos "from the whole world," from he oikoumene ge "the inhabited world (as known to the ancient Greeks); the Greeks and their neighbors considered as developed human society (as opposed to barbarian lands)," in later use "the Roman world" and in the Christian sense in ecclesiastical Greek, from oikoumenos, present passive participle of oikein "inhabit," from oikos "house, habitation" (from PIE root *weik- (1) "clan"). Related: Ecumenic.

word-forming element making nouns implying a practice, system, doctrine, etc., from French -isme or directly from Latin -isma, -ismus (source also of Italian, Spanish -ismo, Dutch, German -ismus), from Greek -ismos, noun ending signifying the practice or teaching of a thing, from the stem of verbs in -izein, a verb-forming element denoting the doing of the noun or adjective to which it is attached. For distinction of use, see -ity. The related Greek suffix -isma(t)- affects some forms.