occasional only before noun (happening sometimes, but not often or regularly): I receive occasional phone calls from him.
sporadic written (happening only occasionally, but not regularly): We still hear sporadic gunfire during the night.
intermittent (happening with periods in between, but not regularly): There will be intermittent showers throughout the night.
odd only before noun (happening in a way that is not expected, regular, or planned): David does odd jobs; he barely makes enough to eat.
periodic only before noun (happening repeatedly over a period of time): We will experience periodic heavy showers and sunshine on Sunday.