ecclesiologyEnglishOxford New American Dictionaryecclesiology /əˌklēzēˈäləjē, əˌkliziˈɑlədʒi / ▸ noun 1 the study of churches, especially church building and decoration. 2 theology as applied to the nature and structure of the Christian Church. – DERIVATIVES ecclesiological /iˌklēzēəˈläjikəl/ adjective,ecclesiologist /-jist/ noun– ORIGIN mid 19th century : from Greek ekklēsia ‘assembly, church’ + -logy.