*congregational*

n. 1. That system of church organization which vests all ecclesiastical power in the assembled brotherhood of each local church. [ 1913 Webster ]

2. The faith and polity of the Congregational churches, taken collectively. [ 1913 Webster ]

☞ In this sense (which is its usual signification) Congregationalism is the system of faith and practice common to a large body of evangelical Trinitarian churches, which recognize the local brotherhood of each church as independent of all dictation in ecclesiastical matters, but are united in fellowship and joint action, as in councils for mutual advice, and in consociations, conferences, missionary organizations, etc., and to whose membership the designation “Congregationalists” is generally restricted; but Unitarian and other churches are Congregational in their polity. [ 1913 Webster ]