ceiling

(noun) the overhead upper surface of a covered space. Example: "He hated painting the ceiling."

(noun) (meteorology) altitude of the lowest layer of clouds.

(noun) an upper limit on what is allowed. Synonyms: roof, cap. Examples: "He put a ceiling on the number of women who worked for him." "There was a roof on salaries." "They established a cap for prices."

(noun) maximum altitude at which a plane can fly (under specified conditions).