Amusement is a feeling of being entertained and happy. Just think about how you feel when you visit an amusement park, and you will get the idea.
When something amuses you, it makes you laugh, holds your attention, entertains you, or all three. An amusement is an activity that produces that type of feeling. Watching a basketball game and flying a kite are amusements. Also, doing something fun fills you with the emotion of amusement. To amuse is to entertain, and when you add the suffix -ment to the end of the verb, you get the noun or the feeling you gain from being amused.