Definitions of extra:

• noun:   something additional of the same kind

  Example: "He always carried extras in case of an emergency"

• noun:   an additional edition of a newspaper (usually to report a crisis)
• noun:   a minor actor in crowd scenes
• adjective:   added to a regular schedule
• adjective:   further or added

  Example: "Need extra help"

• adjective:   more than is needed, desired, or required

  Example: "Found some extra change lying on the dresser"

• adverb:   unusually or exceptionally

  Example: "An extra fast car"