"Most semitropical" refers to an area or climate that is slightly tropical or subtropical. However, if we are looking for antonyms for this term, we would be looking for words that describe areas or climates that are not at all tropical or subtropical. Some antonyms for "most semitropical" could include terms such as arctic, frigid, icy, polar, and cold. These antonyms imply a climate that is very different from a semitropical one and may be characterized by snow, ice, and extreme cold temperatures. Ultimately, the word antonyms show us the opposite of what the original term means, and in this case, it highlights the opposite of a semitropical climate.