system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why are bedroom & bathroom each one word, but living room and dining room are two?
gpt
Very simple. 
The reason for this is that 'living' and 'dining' are verbs, while 'bed' is a noun.
Verbs: A word used to describe an action, state, or occurrence, and forming the main part of the predicate of a sentence, such as hear, become, happen.
Nouns: A noun is the name of a person, place, thing, or idea.