Semi-occasional refers to something that happens or occurs at irregular intervals. The antonyms for this word are regular, frequent, constant, consistent, habitual, and routine. These words describe actions or events that occur at fixed and predictable times. Regular implies conformity to a set pattern or schedule, whereas frequent suggests an event or action that happens often. Constant, consistent, and habitual all refer to actions or events that happen regularly and without interruption. Routine, on the other hand, implies a fixed pattern of behavior that occurs regularly. In contrast, semi-occasional refers to a more random and unpredictable pattern of occurrence.