The word "un-firm" is essentially a negation of the word "firm", which means strong, solid, or stable. Antonyms for "un-firm" would, therefore, include words that describe the opposite characteristics. Some of the antonyms for "un-firm" include unsteady, unstable, shaky, weak, flimsy, wobbly, and insecure. These words describe things or situations that lack stability, are easily shaken or unstable, and may be unreliable. The opposite of firm could also include words such as fickle, vacillating, or indecisive. The use of appropriate antonyms for "un-firm" helps provide a clearer understanding of the context in which the word is being used.