The word "nonmeaningful" implies a lack of significance, purpose or value. Its antonyms, on the other hand, refer to words that convey the opposite meaning. To replace "nonmeaningful," one could use significant, profound, valuable, meaningful, purposeful, or relevant. These words all indicate that the subject in question holds importance or bears significance. For instance, if someone were to claim that a particular activity was nonmeaningful, the antonym would suggest that the activity had purpose or value. Using antonyms of nonmeaningful can lend depth and richness to one's language, by imbuing it with a sense of importance and significance.