The opposite or antonym of "in-firmest" is "strongest" or "firmest." When we say someone is in-firm, it means they are weak, feeble, or frail. So, the antonyms for in-firmest would be words like robust, powerful, sturdy, or unyielding. Someone who is physically fit and healthy would be strong or firm, while someone who is in-firm would be weak or fragile. Similarly, when we talk about business or market conditions, a strong market or economy would be the opposite of an in-firm or weak one. Overall, in-firmest is a term that describes a state of physical or emotional weakness, and its antonyms represent a variety of words that describe strength or firmness.