As an adjective, the word [coed](http://en.wiktionary.org/wiki/co-ed#Adjective), short for coeducational, indicates an institution that teaches both males and females. However, [as a noun](http://en.wiktionary.org/wiki/co-ed#Noun), it can only mean "a young **woman** who attends college". Why is this so and how did this come about?