Semioccasionally refers to something that occurs at irregular intervals, that is not very frequent but still happens from time to time. Its antonyms include frequently, regularly, often, always, and habitually. Frequently refers to an action that happens often or repeatedly, while regularly means that something is done on a set schedule or routine. Often is used to describe an action that happens many times, while always suggests that something happens without fail. Habitually means that something is done as a habit or a custom. All these antonyms contradict the meaning of semioccasionally, which conveys irregularity, infrequency, and unpredictability.