The antonyms for the word "in variable" are "constant," "consistent," "predictable," and "stable." These words represent a state of being that does not change or vary. A constant factor is one that remains the same over time, while a predictable outcome can be expected to occur. Consistency suggests a regularity and reliability, and stability refers to a state of being firmly fixed in place. These antonyms can be useful when describing a situation or phenomenon where variability or unpredictability is undesirable, and a stable or predictable state is preferable.