The word "unthematic" refers to something that lacks a clear or central theme. Hence, the antonyms for this word would be "thematic," "cohesive," "meaningful," and "purposeful." When something is thematic, it is characterized by a central idea or concept that ties all parts together. On the other hand, when something lacks a theme, it is often disjointed, scattered, and lacking in coherence. Cohesive, meaningful, and purposeful are other antonyms for "unthematic," as they suggest that something is unified, significant, and serving a clear purpose. These antonyms are useful in identifying the opposite qualities of something that is not thematic, providing clarity and focus to a subject.