Some commonly used prefixes in English are anti-, de-, dis-, non-, mis-, pro-, sub-, semi-, pre-, post-, trans-, tri-, inter- and micro-. When attached to the beginning of a word, these common prefixes indicate the meaning of a world or change the meaning of the word.
The prefix "semi-" means "half of" or "part." When added to the word"circle," "semi-" changes the meaning of the original word to mean half a circle. Another example is the prefix "trans-" which means "across," "beyond" or "through." Thus, when "trans-" occurs at the beginning of the word "Atlantic" to form "Transatlantic," the resulting word means "across the Atlantic."