Relating to a congregation or assembly of people; involving or consisting of members gathered together, especially in a church context.
From 'congregation' plus the suffix '-al' (relating to), with roots in Latin 'congregatio' (a gathering, assembly).
You'll see this word in 'Congregational church' (a type of Protestant Christianity) and 'congregational singing' (where everyone sings together), meaning it involves the whole group acting together.
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