How to say "indoor" in Japanese

• 室内しつないCommon
  no-adjectiveThe default word for the literal sense: the space inside a room or building. Choose it when saying that something happens, is kept, or is located indoors rather than outside.
  たとえ外そとはどんなに寒さむくとも、室内しつないは気持きもちよく暖あたためられている。↗

  No matter how cold it is outside, the rooms are comfortably heated.
• インドアCommon
  nounA katakana loanword from English 'indoor'. It is much narrower than 室内, appearing chiefly in talk of indoor-versus-outdoor lifestyles, as of a person who prefers staying in; for most senses use 室内.

Use 室内 for the literal inside of a room or building and for indoor spaces and activities generally; 「インドア」, a loanword, is narrower, chiefly covering indoor-versus-outdoor lifestyles and people who prefer staying in.

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

• 室内しつないindoor
• インドアindoor