The word "sub-serves" means to be of service, to be useful or advantageous. It is a fairly obscure word and may not have direct antonyms. However, some related antonyms may include harm, hinder, impair, impede, and obstruct. These words refer to actions or conditions that make something less productive, beneficial or advantageous. In contrast, actions or conditions that may serve to improve, enhance or advance can be considered as synonyms of "sub-serves." Such words include aid, assist, benefit, facilitate, and promote. Ultimately, the choice of the appropriate word will depend on the particular context in which it is used.