Put your thumb and first finger out in an L. That corner — the one you also see where a wall meets a floor, or at the corner of a sheet of paper — is the whole idea. English can either name that corner as a thing you count, or use it to describe how two objects are lying against each other. Same L, once as a noun you point at, once as a way of placing things.
把大拇指和食指張成一個 L。那個角落——你在牆和地板相接的地方、在紙張的角上也看得到的那個——就是這個詞的全部。英文可以把那個角當成一個東西來數，也可以拿它來描述兩樣東西互相擺放的方式。同一個 L，一次是你指得出來的名詞，一次是擺放的講法。
From the word’s history
Recorded as a calque of Latin angulus rectus; rectus carries the sense of straight or upright, so right here is about being straight, not about being correct.
來源記載這個詞是拉丁文 angulus rectus 的直譯。rectus 是「直的、正的」，所以 right 在這裡指「直」，不是「正確」——這正好對上上面那個 L 的畫面。
Wiktionary entry supplied in this packet (etymology_text on right angle, noun): Calque of Latin angulus rectus.