From the word’s history

out- + door.

由 out- 加上 door 組成。

Wiktionary

Picture past the door of a building. Outdoor is everything on that side: the open air, under the sky, not shut inside walls and a roof.

可以想成:跨出建築物那道門之後的世界。門裡是室內,門外就是 outdoor——露天、在天空底下、不被牆和屋頂圍住的地方。

One branch

門外・露天

登入就可以看這一支怎麼連回核心畫面。

outside, not indoors · adjective

Happening, existing, or used outside, not inside a building.

戶外的