noun, noun which may take the genitive case particle 'no'
inner wall; interior wall
Refers to the inside surface of a wall, or a wall inside a building or structure. Often used in architectural, medical, or technical descriptions.
There is a crack in the inner wall of the building.
The paint on the interior wall has started to peel.
Compound of 内 (nai, 'inside') and 壁 (heki, 'wall'). The reading is on'yomi, and the word is a straightforward Sino-Japanese compound.