Functional clothing provides the human body protection against weather — strong sunlight, extreme heat or cold, and precipitation — also protection against insects, noxious chemicals, weapons, and contact with abrasive substances. In sum, clothing protects against anything that might injure the naked human body. Non-functional clothing would be the opposite, I believe.
New words, one handy idiom, and a 2-minute quiz — delivered to your inbox to keep your streak alive.