The Latin word extra means outside, and this prefix forms the beginning of many English words implying a meaning of outside or beyond.
Here are some examples of "extra" words.
extra-curricular (adjective) - not forming part of the normal curriculum. For example, "My daughter participates in several extra-curricular activities at school, including hockey and community service."
extradite (verb) - to hand over a person (accused or convicted of a crime) to a foreign country or state in which the crime was committed. For example, "The accused man was extradited to the United States".
extramural (adjective) - additional to normal teaching or studies, expecially for non-resident students.
extraneous (adjective) - of external origin. A pearl is formed around an extraneous particle, often a grain of sand.
extrapolate (verb) - to infer values of a variable in an unobserved or unknown interval from values within an already observed value. Extrapolation is a process of projecting, extending or expanding known information to make an educated guess or prediction. For example, you could extrapolate population data on Australia to predict the population in 2010.
extraterrestrial (adjective) - outside the earth or its atmosphere. Extraterrestrial beings are often the subject of science fiction novels or films. Steven Spielberg's E.T. film is perhaps the best known.