IPA: /ˈhɛdruːm/
KK: /ˈhɛdˌrum/
The amount of vertical space available above a person or object, allowing for movement without hitting the ceiling or other overhead structures.
Make sure there is enough headroom in the room so that people can stand comfortably without bumping their heads.
Headroom is formed from "head" (from Old English "heafod", meaning the upper part of the body or the leader) and "room" (from Old French "rom", meaning space or area). The word "headroom" refers to the space above one's head, particularly in a confined area, allowing for movement without obstruction.
Think of the 'head' as the upper part of the body needing 'room' or space above it — that's why 'headroom' means the space above your head.