For knights of old, it helped to save face (5)
I believe the answer is:
visor
'face' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Maybe you can see a link between them that I don't see?
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for visor that I've seen before include "Face-protector" , "Front piece of a helmet" , "Movable front part of helmet" , "Helmet's face-cover" , "Face guard; sun screen" .)