外|がいgai[1]atamadaka (head-high)

1. suffixoutside ...; beyond ...; not included in ...
   それは私の研究けんきゅう外がいのことです。↗

   It is outside my area of study.

• SynonymアウトサイドNeutralA katakana loanword for the outer side of something; mostly heard in sports, e.g. an outside corner in baseball. A standalone noun, not a suffix like 「外」.
• Related表面ひょうめんNeutralRefers to the surface of a thing, as in 「表面上は」; it stresses the outer layer rather than being outside a range or scope.
• Related表おもてNeutralRefers to the front of something or the outdoors, as in 「表に出る」; it stresses the front side rather than being beyond a range.
• AntonymうちNeutralThe opposite of 「外」: inside, within, or a stretch of time, as in 「家のうち」. As a suffix it is read 「ない」 in 「〜内」.

Attach 「〜外（がい）」 to a noun for outside or beyond a range, as in 「予想外」「専門外」「時間外」; for within a range say 「〜内（ない）」. For a physical outer side (esp. sports) use アウトサイド, for a surface 表面, for the front or outdoors 表.

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

1. （ガイ）そとがわ。含ふくまれない。属ぞくさない。範疇はんちゅうにない。
2. 外国がいこく、異国いこくの意味いみを持もつ熟語じゅくごを作つくる。
3. 母方ははかた、女系じょけいの意味いみを持もつ熟語じゅくごを作つくる。