Use 'sporadically' to describe events that don't follow a pattern or fixed schedule. The old bus arrives sporadically, so it's not reliable for daily commute.
Pro Tip 2/3
Not Continuous
'Sporadically' indicates breaks in continuity, suggesting something starts and stops at irregular intervals. She only checks her email sporadically, which means she might miss urgent messages.
Pro Tip 3/3
Unpredictability
Something that happens sporadically is often unpredictable, without warning or signs. Meteor showers can occur sporadically, making them exciting yet hard to anticipate.