Silly (adjective)

1. Foolish or lack of good judgement.
2. Childish or immature.
3. Unreasonable or absurd.
4. Entertainingly ridiculous.
5. Amusing or lighthearted.

Origin:

Middle english sely "innocent, blessed", from old english salig "blessed".

Examples:

1. The silly prank played by the boys caused everyone to laugh.
2. She had a silly habit of talking to herself.
3. His silly comments made everyone roll their eyes.
4. The movie was filled with silly gags that had everyone in stitches.
5. The silly hat he wore to the party made everyone smile.