[adjective]Is the central heating functional yet (= is it working as it should do)?(specialized) He's suffering from a functional disorder of the ear (= his ear is not working correctly, although it has not been damaged by a physical injury).(specialized, esp. US) It's time something was done about the number of functional illiterates/the rates of functional illiteracy (= the number of people who are able to live and possibly work in society, but who cannot read and write) in this country.
FUNCTIONAL
Meaning of FUNCTIONAL in English
Cambridge English vocab. Кембриджский английский словарь. 2012