(eks′trə) adjective
Being over and above what is required; additional.
—noun
1. Something beyond what is usual or required.
2. A copy or an edition of a newspaper issued for some special purpose, or at a time different from that of the regular edition.
3. In cricket, any run resulting from a by, leg–by, no–ball, or wide.
4. Something of a special quality.
5. An actor, not a member of the regular cast, hired for a special scene, as a mob scene, or for a small part.
—adverb Unusually. [<L, outside, beyond]

Beyond; outside; outside the scope of: extraordinary beyond the ordinary; extra–oral outside the mouth. [<L extra-<extra <exter on the outside <ex out]
Extra– may appear as a prefix in hyphemes or solidemes, as in: