The term "more subitaneous" implies something that is sudden or unexpected. Its antonym, therefore, would be a word that suggests a gradual or predictable change. Some possible antonyms include "gradual," "slow," "orderly," "routine," or "planned." For instance, if someone were to ask for an antonym for the phrase "more subitaneous," one could respond with the word "gradual," connoting a change that is slow and steady rather than sudden and unexpected. Similarly, one could use the word "routine" to suggest something that happens according to a set order or pattern, rather than catching people off guard.