the word unhappy is a straightforward english formation, combining the native old english negative prefix un- with the adjective happy. happy itself entered middle english from the old norse word 'happ', meaning "chance, good luck," which is related to the old english 'gehæp', meaning "fit, convenient." the prefix un- is one of the most common and productive means of negation in english, directly reversing the quality of the root word. thus, the literal construction "not happy" has transparently evolved to describe the state of sadness or misfortune.

Structure: un (not) + happy (feeling pleasure) un- is a prefix of Old English origin, meaning "not," used to give a negative or opposite force. happy is an adjective of Middle English origin (from hap + -y), meaning "fortunate, pleased."