開催[kaisai] holding a meeting
開催式[kaisaishiki] opening ceremony (of an event, show, etc.)
開催中[kaisaichuu] in session
共催[kyousai] joint sponsorship
催し[moyooshi] event

催物[moyoushimono] points of interest
催す[moyoosu] to hold (a meeting)
催淫剤[saiinzai] aphrodisiac
催合う[moyau] to co-operate (in enterprises)
催告[saikoku] notification