Antonyms for "most reassuring" would be words that indicate doubt, fear, and uncertainty. Some of the antonyms for "most reassuring" are words like alarming, unsettling, worrying, disturbing, unsettling, and unnerving. These words convey a sense of unease and apprehension, and they can make people feel uneasy or anxious. Additionally, terms like unreliable, unsound, doubtful, dubious, unconvincing, and untrustworthy convey a lack of credibility and reliability. If you want to express the opposite of "most reassuring," these are the words you could use to achieve that goal.