in‧door /ˈɪndɔː $ -ɔːr/ adjective [only before noun]
used or happening inside a building Antonym : outdoor:
an indoor swimming pool
the world indoor athletics championship
Too much central heating can harm indoor plants.


GRAMMAR
indoor, indoors
Indoor is an adjective and indoors is an adverb:
I stayed indoors (NOT indoor).
indoor sports (NOT indoors sports)

[TahlilGaran] Dictionary of Contemporary English ▲

indoor
adjective
BAD: As it was raining we decided to stay indoor.
GOOD: As it was raining we decided to stay indoors.

Usage Note:
Indoor (WITHOUT s ) is an adjective: 'an indoor tennis court', 'indoor athletics'.
Indoors (WITH s ) is an adverb: 'I don't like spending the whole day indoors.'

[TahlilGaran] Dictionary of Common Errors ▲