indoor

indoor — adjective

1. describing something that exists, happens, or is kept within a building rather t

1.adjectiveA2
Definition

describing something that exists, happens, or is kept within a building rather than in the open air

Example

The children played indoor games all afternoon because it was raining outside.

indoor + noun (games) for activities inside

Mizuki prefers indoor sports like badminton and table tennis.

indoor + noun (sports) for athletic activities

Common collocations
  • indoor pool
  • indoor market
  • indoor activities
  • indoor games
  • indoor plants
  • indoor sports
  • indoor space
  • indoor arena
  • indoor grill
  • indoor theatre
Synonyms
  • interior

    more formal and technical; typically describes the inside surface or space of a structure rather than activities — e.g. 'interior decorating'

  • covered

    narrower meaning, focusing on having a roof overhead — e.g. 'covered market' rather than any indoor space

  • enclosed

    emphasises being surrounded by walls or fencing; can include outdoor spaces like patios that are walled in

Antonyms
  • outdoor

    the direct opposite; refers to anything happening or used in the open air

  • outside

    more general; can also function as a preposition or adverb

Grammar Patterns

indoor + noun

Usage Note

Attributive only — indoor must be placed directly before the noun it modifies (indoor pool, indoor market). Do NOT use it after a linking verb: ✗ 'The pool is indoor.' ✓ 'The pool is indoors.' — indoors is the adverb form used in predicative or adverbial positions.

Common Mistakes

We stayed indoor because of the rain.
We stayed indoors because of the rain.
indoor is an adjective used before nouns; the adverb indoors is needed after a verb.
This restaurant is indoor.
This is an indoor restaurant.
indoor cannot follow a linking verb; it must come before the noun it describes.

Word family

Synonym discussion

Sense: adjective/1

All four words describe something that is not fully exposed to the open air, but they differ in scope and use. Indoor is the everyday word for any activity, object, or space located inside a building — it is always placed before a noun (indoor pool, indoor market). Interior is more formal and usually refers to the inner part or surface of something (interior walls, interior design), rather than to activities or uses. Covered focuses specifically on having a roof or overhead shelter — a covered stadium has a roof but may be open on the sides, whereas an indoor stadium is fully enclosed. Enclosed emphasises being surrounded by walls, fencing, or other barriers — an enclosed garden has walls but is still outdoors. For a learner, indoor is the safest and most frequent choice for everyday situations; the others suggest a narrower or more technical angle.

indoor ↗interior ↗coveredenclosed

Common collocations

Nouns

Phrases

  • indoor and outdoor
  • indoor or outdoor

Etymology

Old EnglishMiddle EnglishEnglish

Formed in English around the early 1600s from the preposition in and the noun door, originally meaning 'within the house' — the door being the boundary between inside and outside. The spelling was originally two words (in door) or hyphenated (in-door) before settling as a single compound adjective by the 19th century.