Looking up...
Il soffitto della stanza è molto alto.
The ceiling of the room is very high.
The upper interior surface of a room or other enclosed space.
Hanno dipinto il soffitto di bianco.
They painted the ceiling white.
Il soffitto della cappella è decorato con affreschi.
The chapel's ceiling is decorated with frescoes.
In architecture, 'soffitto' can also refer to the underside of a structural element like a bridge or arch.
Think of 'soffitto' as the ceiling INSIDE a room (under your feet when you look up), while 'tetto' is the roof OUTSIDE (protecting you from above).
From Latin *suffictus*, past participle of *suffigere* 'to fasten underneath', from *sub-* 'under' + *figere* 'to fix'.
In Italian, 'soffitto' is the standard term for the interior ceiling of a room. For the exterior roof (the covering of a building), use 'tetto'.