Outside means beyond the limits or boundaries of something, or relating to the exterior. It functions as a preposition (outside the room), an adverb (go outside), a noun (the outside of the building), and an adjective (an outside wall).
What Does Outside Mean?
Outside is formed from the Old English components ut ("out, away from the interior") and side ("a surface or edge"). The compound first appeared in English in the 16th century as a noun meaning "the outer surface", before developing its prepositional and adverbial senses. The word is one of the most frequent in everyday English — the Oxford English Corpus lists it among the top 500 most common words.
As a preposition, outside expresses position or movement beyond a boundary: outside the classroom, outside working hours. As an adverb, it stands alone to describe a location away from the interior: it is cold outside, shall we sit outside? As a noun, it refers to the exterior surface or area: the outside of the envelope. As an adjective, it describes something positioned on the exterior, or originating from beyond a group: an outside toilet, an outside expert.
The language learner's key focus should be the preposition use, particularly the British English rule that outside — unlike outside of in American English — is used without of in standard formal writing.
Example Sentences (A2 → C1)
| Sentence | Level & usage note |
|---|---|
| There is a dog waiting outside the door. | A2 — preposition; basic location |
| She tried to use English outside the classroom as much as possible. | B1 — preposition; figurative boundary |
| It is getting dark outside, so let us head home. | B1 — adverb; standalone, informal |
| The committee decided to seek outside expertise rather than rely solely on internal staff. | B2 — adjective; formal/professional context |
| Beyond its immediate political implications, the ruling has consequences that extend well outside the jurisdiction of any single nation state. | C1 — preposition; complex noun phrase, academic register |
Collocations
| Collocation | Example |
|---|---|
| outside world | Prisoners often feel cut off from the outside world. |
| outside chance | There is an outside chance the flight will be delayed. |
| outside interests | She has many outside interests, including photography and cycling. |
| outside hours | You can email us outside office hours. |
| outside help | We brought in outside help to speed up the project. |
| think outside the box | We need to think outside the box to find a solution. |
| go/come outside | Come outside — it is a beautiful afternoon. |
| wait outside | Please wait outside while we prepare the room. |
| outside the classroom | Language learning happens outside the classroom too. |
| on the outside | The cake looks perfect on the outside but it is raw in the middle. |
Usage Notes
- British vs American English: In British English, use outside the building (no of). In American English, outside of the building is equally common. Both are understandable worldwide, but in formal British writing, drop of.
- Preposition or adverb? If outside is followed by a noun phrase, it is a preposition: outside the school. If it stands alone, it is an adverb: Let us go outside.
- Noun use: The noun outside almost always takes the definite article: the outside of the box. Using it without the (e.g. outside of box) sounds unnatural.
- Idiom alert: Think outside the box (= think creatively) is extremely common in business English but is considered a cliché in formal writing. Use with care.
Common Mistakes
Watch Out For
She waited outside of the station for an hour. (British formal writing)
She waited outside the station for an hour. (standard British English — no "of")
The outside of a building is very beautiful.
The outside of the building is very beautiful. (use "the" with a specific referent)
I need go outside for fresh air.
I need to go outside for some fresh air. ("go" requires "to" as part of the infinitive)
Etymology
Outside is a compound of out (Old English ut, meaning "away from the interior, outward") and side (Old English side, meaning "a flank, surface, or edge"). The compound is attested from the early 16th century, initially as a noun denoting the outer surface of an object. The prepositional use — meaning "beyond the boundary of" — followed in the 17th century, and the adverbial use became firmly established by the 18th century. Related formations include insider, outsider, and outside in (turned so that the outer surface faces inward).