The phrase "imageless thought" refers to a mental concept or idea that does not involve any visual imagery. Synonyms for this term might include "abstract idea," "pure concept," or "non-visual thought." Some other possible options could be "formless cognition," "imagery-free notion," or "thought without imagery." These phrases all capture the essence of the idea of a thought or concept that is not tied to any particular visual representation. Whether discussing philosophical or scientific concepts, creative ideas, or personal beliefs, these synonyms can help to clearly communicate the idea of a thought that exists purely in the abstract realm of consciousness.