describes a grammatical structure, such as a word PREFIX or SUF-FIX, that can easily combine to form new words or phrases. For example, the negative prefix un-is highly productive; not only can many new words be formed with it, but other speakers of English will be able to understand the word without further explanation. You could tell a friend that your blind date last night was “very unwonderful,†and although the word is not in the dictionary and may never have been heard before, your friend would understand it immediately.