How to say "add-on" in Japanese

• アドオン
  nounThe loanword for a software add-on: extra software installed into a browser, program, or game to add features. It denotes the added component itself, not the add-on approach or any sum of money.
• アドオン方式アドオンほうしき
  nounAdds 方式 'method, system' to the loanword, so it names the add-on approach or architecture — extending a base system with add-ons — rather than an individual add-on; typical of technical discussions of system design.
• 追加額ついかがく
  noun額 means an amount of money, so this is for the financial sense of 'add-on': an extra sum or charge added on top of a base amount. It is not used for software features.
• 機能拡張きのうかくちょう
  nounA Sino-Japanese term meaning 'extension of functionality', covering software extensions, add-ons, and plug-ins. It suits contexts where the point is expanding what a program can do rather than the add-on as a product.

For software add-ons, choose 「アドオン」 or 機能拡張; 「アドオン方式」 names the add-on approach or architecture, while 追加額 is only for an added amount of money.

Usage comparisons are AI-assisted and cross-checked by multiple models; for study reference only

• アドオンadd-on
• アドオン方式アドオンほうしきadd-on
• 追加額ついかがくadd-on
• 機能拡張きのうかくちょう(software) extension