The phrase "be no avail" means that something is useless or ineffective. There are several antonyms for this phrase, including "have an effect," "make a difference," and "be effective." These antonyms suggest that the action or effort put forth will have a positive impact and achieve the intended result. Other antonyms include "succeed," "work," and "be fruitful," which imply that the outcome of the effort is successful and beneficial. Using these antonyms instead of "be no avail" helps to convey optimism and hopefulness in achieving a desired result.