Fun is defined by the Oxford English Dictionary as "Light-hearted pleasure, enjoyment, or amusement; boisterous joviality or merrymaking; entertainment". Etymology and usage The word fun is associated with sports, entertaining media, high merriment, and amusement. Although its etymology is uncertain, it has been speculated that it may be derived from Middle English (fool) and (the one fooling the other). An 18th century meaning (still used in Orkney and Shetland) was "cheat, trick, hoax", a meaning still retained in the phrase "to make fun of". The way the word fun is used demonstrates its distinctive elusiveness and happiness. Expressions such as "Have fun!" and "That was fun!" indicate that fun is pleasant, personal, and to some extent unpredictable. Expressions such as "I was making fun of myself" convey the sense that fun is something that can be amusing and not to be taken seriously. The adjective "funny" has two meanings, which often need to be clarified between a speaker and listener. One meaning is "amusing, jocular, droll" and the other meaning is "odd, quirky, peculiar". These differences indicate the evanescent and experiential nature of fun and the difficulty of distinguishing "fun" from "enjoyment". Fun's evanescence can be seen when an activity regarded as fun becomes goal-oriented. Many physical activities and individual sports are regarded as fun until the participant seeks to win a competition, at which point, much of the fun may disappear as the individual's focus tightens. Surfing is an example. If you are a "mellow soul" (not in a competition or engaging in extreme sport) "once you're riding waves, you're guaranteed to be having fun". The pleasure of fun can be seen by the numerous efforts to harness its positive associations. For example, there are many books on serious subjects, about skills such as music, mathematics and languages, normally quite difficult to master, which have "fun" added to the title. Activities Many physical activities provide opportunities to play and have fun. Not only can these activities be fun, but can also improve physical and mental states. Psychology According to Johan Huizinga, fun is "an absolutely primary category of life, familiar to everybody at a glance right down to the animal level." Psychological studies reveal both the importance of fun and its effect on the perception of time, which is sometimes said to be shortened when one is having fun. As the adage states: "Time flies when you're having fun".