Continually occurring; persistent. Regularly recurring: plagued by constant interruptions. Unchanging in nature, value, or extent; invariable. See Synonyms at continual. Steadfast in purpose, loyalty, or affection; faithful. See Synonyms at faithful. Something that is unchanging or invariable. A quantity assumed to have a fixed value in a specified mathematical context. An experimental or theoretical condition, factor, or quantity that does not vary or that is regarded as invariant in specified circumstances.