1.
lintel; upper door rail
in traditional Japanese architecture, the horizontal wooden beam above a doorway or opening that contains the upper groove for sliding doors (fusuma or shoji)
Architecture
The 鴨居 is the upper horizontal beam in traditional Japanese rooms, while the 敷居 (threshold) is the lower beam. Together they form the frame for sliding doors like 襖 and 障子.
Cultural note
Older Japanese houses often have low 鴨居, designed for people of shorter average height in earlier eras. Tall visitors frequently bump their heads.