theoreticalEnglishOxford American Thesaurustheoretical adjective 1 theoretical physics: not practical, conceptual, abstract, pure. ▷antonyms practical, applied. 2 a theoretical possibility: hypothetical, conjectural, academic, suppositional, speculative, notional, postulatory, conjectured, imagined, assumed, presumed, untested, unproven, unsubstantiated; rare suppositious, suppositive, ideational. ▷antonyms concrete, actual, real.