Nonsequential refers to a lack of order or sequence. Therefore, antonyms for nonsequential might include words that denote order or sequence, such as sequential, chronological, consecutive, or ordered. These words all convey the idea of things happening in a specific order or following a predetermined pattern. Other antonyms might include words that connote planning or arrangement, such as organized, structured, systematic, or methodical. These words all suggest a deliberate and intentional approach to organization and order, in contrast to the randomness and lack of planning implied by nonsequential. By using these antonyms, one can describe a situation or process that is well-organized, well-planned, and orderly.