Extemporary

ad hoc ad lib at first glance automatic by ear casual expedient extempore free immediate impromptu improv improvisatory improviso informal jamming made-up makeshift offhand off the cuff off the top of head on impulse on-the-spot snap spontaneous spur-of-the-moment taking for ride thought out loud tossed off tossed out unplanned unpremeditated unprepared unstudied winging it