The word "sur-plusser" is not present in the English language, hence there are no antonyms for it. However, it is possible that the word is a misspelling of the word "surpasser," which means to exceed, excel or outdo. Antonyms for surpasser could include words such as "underachiever," "inferior," "substandard," "mediocre," or "laggard." These words denote the opposite of surpassing, falling short of expectations or failing to meet desired standards. It's important to note that clarity in language is vital to ensure effective communication and that incorrect spellings can result in misinterpretation.