A gathered group practising together, small enough that everyone is known. Its root is the same as convene — a coven is people who come together.
Old French covent (a gathering, assembly), from Latin conventus, past participle of convenire (to come together), from com- (together) + venire (to come); a gathered group small enough that everyone in it is actually known to the others.
A gathered group practising together, small enough that everyone in it is known. It shares its very root with convene — people who came together, nothing more mysterious than that.