Translation guide
How to express 'outer' in Japanese depends on what is being described. The most common word is 外側 (sotogawa) for the outer side or exterior of a physical object. For abstract or relational uses, other expressions like 外部 (gaibu) or 外 (soto) are more natural.
Describing the outside surface, layer, or part of something concrete.
The most common and neutral word for the outer side or exterior of a physical object. Used for things like boxes, buildings, clothing, etc.
箱の外側にラベルを貼ってください。
Please put the label on the outer side of the box.
外側の壁は白く塗られている。
The outer wall is painted white.
A more general word for 'outside'. Can be used for the outer part of something, but is less precise than 外側. Often used in compound words.
外ポケットに鍵を入れた。
I put the key in the outer pocket.
Referring to something outside a group, system, or organization, or an external factor.
Used for external factors, outside parties, or the exterior of a system. Common in business and technical contexts.
外部からのアクセスを制限する。
Restrict access from the outside.
外部の専門家に相談した。
We consulted an external expert.
Can also be used for abstract 'outside', but is more casual and less formal than 外部.
外の人間にはわからない。
Outsiders wouldn't understand.
Referring to the vast outside beyond Earth or a contained environment.
Literally 'outer space', used in scientific or sci-fi contexts. Less common than 宇宙 (uchuu) for general 'space'.
外宇宙からの信号を探知した。
We detected a signal from outer space.
Describing the outermost piece of clothing.
Means 'outer garment' or 'jacket'. The standard word for a piece of clothing worn over others.
寒いので上着を着てください。
It's cold, so please put on an outer layer.
Loanword from English 'outer', used in fashion contexts for outerwear like coats and jackets.
このアウターは軽くて暖かい。
This outerwear is light and warm.