The prefix un- is the core of a joke in Poul Anderson's science fiction story Un-Man. The character is the United Nations cloned super-soldier UN Man, referred to as unman by his opponents. UN can be short for United Nations, but also in English is two prefixes. Both of these prefixes are from Old English. In this use unman, the noun means someone who is not human. Although that isn't what it would mean in the context of being unmanned. For a place to be unmanned means that no one is working there. The verb to unman someone means to make them lose their courage and is related to unmanly, meaning to not behave like a man is expected to.
The first un- prefix means not, as in not happy being unhappy. It is the most common prefix in the English language and comes unchanged from Old English. It seemed to die out in written sources during the time the Norman French ruled England (1066 to 1485). However it came back strongly as more English speakers started writing again. There are many thousands of words that use un- to mean not. This prefix is so common in English that it can even be added to phrases and be easily understood. For example: uncalled-for and undreamed-of.
The second un- prefix is to reverse an action, as in to take things out of this packed box or unpack. Like the first un- prefix, it also comes from Old English. There can be confusion between these two prefixes. Does an unlocked door mean that it was not locked or that it was locked and that one has opened the lock? The reader must decide which meaning is intended from context. Is your shirt unbuttoned because you did not button it or because you undid or reversed the buttoning?
There are even more prefixes that mean not. These include in- as in intolerant; non-, as in nonsense; anti-, as in anti-bacterial and counter- as in counterclaim. There is also the prefix dis- as in discount, but this prefix is also spelt dys- and de- as in dysentery and decode. In contrast to the un- prefix, all of these are of Latin/French origin. Next time, I will examine the in- prefix and then the problems between un- and in-.