These vessels are 'defined' as those that carry blood to the heart and those that carry blood away from the heart. Their general characteristics include that arteries generally carry oxygenated blood and veins generally carry deoxygenated blood , with the exception of the pulmonary artery and veins. The reversal of function is not an exception to their definition but an exception to their characteristics. You mentioned it being an exception to the definition. It's a minute difference and probably doesn't even matter but i just wanted to clear the concepts of the the person making the enquiry.
An earlier typo may have made my answer somewhat hazy, i typed in 'now' instead of 'not'. Quote correction " The pulmonary artery carries deoxygenated blood away from the heart to the lungs and the pulmonary vein returns oxygenated blood to the heart from the lungs. Generally, arteries carry oxygenated blood and veins carry deoxygenated blood but that is 'NOT' how they're defined.
Again, it's a minor difference but i wanted the person asking to have a clear concept of it.