The term 'top-grade' refers to something that is of the highest quality or standard. Antonyms of 'top-grade' include words such as 'inferior', 'low-quality', 'substandard', 'poor', and 'second-rate'. These words indicate that the quality or standard of a product, service, or performance, falls short of excellence. For instance, a low-quality product might be associated with an inferior rating, while a substandard service might receive negative feedback. Knowing antonyms of 'top-grade' can help one differentiate between high and low-quality items, services or performances, and choose the best option that meets their requirements.