One way to hold this phrase: a small sign by a front door offering exactly two things and nothing more — a bed for the night, and a breakfast in the morning. The list of two is the whole idea. From there the same words can point at the house that offers it, and, by an older route, at what that night used to cost.
可以想成門口掛著一塊小牌子，上面只提供兩樣東西，多的沒有——一張過夜的床，和隔天早上的一頓早餐。這份「只有兩樣」的清單，就是整個說法的核心。從這裡出發，同樣三個字可以往外指那棟提供服務的房子；還有一條比較舊的路線，指的是這樣住一晚以前要花多少錢。
From the word’s history
Formed from bed plus breakfast, from having a bed for the night and breakfast in the morning on offer.
這個說法由 bed 加 breakfast 組成，來自「提供一晚的床和隔天的早餐」這件事。名字本身就是服務清單，所以三個字合起來的意思，跟字面完全一致。
Wiktionary entry supplied in packet (source_ref kaikki:3f6f69a190036ae4:889346904), etymology_text for etymology 1
登入就可以看每一支怎麼連回核心畫面。