I contacted Merriam-Webster and sent them this definition of "cult"...
Cult - Any organization whose leadership uses mind control on its followers. This applies regardless of the organization's size, or where its members live. Leadership can consist of one person, two people, or multiple people.
I told them that all current definitions suck because they allow too much wiggle room. I told them to look at the FAQ sections of jw.borg and scientology.borg because they both address the "Are we a cult?" question. I told them that The Peoples Temple had one leader, Heaven's Gate had two leaders before Bonnie Nettles died, and Jehovah's Witnesses currently have eight leaders. I told them that they could help a lot since people view Merriam-Webster as an authority. I told them that my definition is probably not politically correct enough for them, but oh well. And I told them to consider revising related definitions for terms like "brainwashing" and "thought/mind control", in light of Steven Hassan's B.I.T.E. model.
Well, that was everything I told them. Probably nothing will come of it but it was worth a shot. Maybe some of you can send a similar message to them using my definition.