the world > relative properties > number > specific numbers > one > only one > [noun] > thing which occurs only once (4)
colloquial. spec. A person who attends church only once on a Sunday. Now rare.
An event, transaction, process, etc., that occurs only once; something that is used or produced only once; a ‘one-off’, esp. a single appearance…
An event which occurs only once or rarely; (also, now chiefly Law) a person who litigates once or only rarely, as opposed to a company, etc…