intransitive verb
Definition: To move up and down in a quick or light manner.
Example: The child watched the cork bob on the surface of the water.
noun
Definition: A quick, jerky movement of the head or body, or a small lock or curl of hair.
Example: She gave a quick bob of her head to show agreement.
transitive verb
Definition: To make something move up and down quickly or to cut something short, like hair.
Example: She decided to bob her hair for a new look.