source: GO-GO~

added to an existing or usual amount or number:

〖名詞の前で〗追加の, 余分の, 特別の, 臨時の

e.g. an extra thirty-five cents an hour.

1. as submodifier to a greater extent than usual; especially:

｟くだけた話｠ 〖形容詞副詞の前で〗格別に, いつもより

e.g. he is trying to be extra good.

2. in addition:

余分に, 追加で, 割り増しで (!主にcost, charge, payなどの〖動詞〗の後で)

e.g. installation will cost about $60 extra.

an item in addition to what is usual or strictly necessary:

(通常･必要以上の)余分(なもの), 予備.

e.g. I had an education with all the extras.

an item for which an additional charge is made:

(標準仕様以外の･追加料金のかかる)オプション製品［サービス］; 追加料金

e.g. the price you pay includes all major charges—there are no hidden extras.

a person engaged temporarily to fill out a scene in a movie or play, especially as one of a crowd:

〘映･テレビ〙 (群衆役などの)エキストラ.

e.g. the film used an army of extras.

dated a special issue of a newspaper:

(新聞などの)号外; 臨時増刊号

e.g. she stood under an awning and read the extra.

mid 17th century (as an adjective): probably a shortening of extraordinary, suggested by similar forms in French and German.