Diamantine is defined as a term for something that is hard, durable, or shining like a diamond. Some synonyms that can be used instead of this word include glittering, sparkling, glistening, luminous, radiant, brilliant, and dazzling. Another option is luminescent, which refers to something that emits light without being heated. Other synonyms to convey the same meaning might be glowing, effulgent, or resplendent. Each of these words could be used in various contexts depending on the context. They can describe the shine of a diamond, the luminescence of stars, or the brilliance of a sunrise.