The term "un did" is not a commonly used term in English language. However, if we break down the word to "un" and "did", we can think of antonyms for both words. The antonym for "un" would be "re" which means "again" or "returning to an original state". The antonym for "did" would be "did not" or "didn't". In essence, "un did" may imply an action that was taken and then undone, conveying a sense of confusion or indecision. Its opposite would therefore be a decisive action that was not undone, giving the impression of certainty and determination.