Additional
Part of speech: adjective
Definition: Supplemental or added to.
Example sentence: A successful society is characterized by a rising living standard for its population, increasing investment in factories and basic infrastructure, and the generation of additional surplus, which is invested in generating new discoveries in science and technology.
Extra
Part of speech: noun
Definition: A run scored without the ball having hit the striker's bat - a wide, bye, leg bye or no ball; in Australia referred to as a sundryan extra edition of a newspaper, which is printed outside of the normal printing cycle
Part of speech: adverb
Definition: To an extraordinary degree.
Part of speech: adjective
Definition: Beyond what is due, usual, expected, or necessary; additional; supernumerary.Extraordinarily good; superior; as extra work, extra pay.
Example sentence: If you're mentally ready, you're willing to go the extra mile.