Respiratory means “to do with breathing, or with the parts of the body that let you breathe.” The respiratory system is your nose, throat, windpipe, and lungs working together. A respiratory illness is one that hits those parts — a cold, flu, asthma, or something more serious. This is a doctor-and-textbook word. You would not usually tell a friend “I have a respiratory problem”; you would say you cannot breathe well, or you have a chest infection. Though actually, respiratory points to the organs and the process, not to the air itself, so “respiratory air” would sound odd. You will see it on medicine boxes and in health news a lot.