The phrase "up to hilt" typically refers to something that is done or used completely or fully. Antonyms for this phrase would include "partially," "incompletely," or "not fully." Other antonyms could include using words such as "vaguely," "loosely," or "lightly," which would suggest that something is not fully or completely done. Another antonym for "up to hilt" could be "halfheartedly," which suggests that someone is putting in a limited effort, rather than being fully committed. Overall, antonyms for "up to hilt" are words that describe incomplete or partial action, rather than something being done completely and thoroughly.