Techo vs. Cielo (raso)
I came across a sentence where ceiling had no choice of Spanish words other than "techo".
It has always been my understanding that techo means 'roof'.
The Spanish word "cielo", however, has a number of meanings:
1) El cielo es azul. (The sky is blue.)
2) Ángeles viven en el Cielo, dicen. (Angels live in Heaven, they say.)
3) Edificios tienen techo y cielo raso. (Buildings have a roof and a ceiling.)
I usually use "techo" for roof and "cielo" for ceiling, but techo can also be used for ceiling:
WordReference is a great resource. It will also usually tell you if the usage is regional rather than standard.
"Techo" also is "cielo raso" (ceiling). If you enter a room with a low ceiling, "¡Cuidado con el techo!". If you try to put a lamp in the ceiling, "¡Cuidado con el techo!"
"Cielo" and "cielo raso" should be accepted as answers but don't panic if the only alternative is "techo". It is right.