The knight of old could see through it easily enough (5)
I believe the answer is:
visor
'the knight' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Maybe they are linked in a way I don't understand?
'old could see through it easily enough' is the wordplay.
I cannot really see how this works, but
'old' could be 'o' (abbreviation as in OT - Old Testament) and 'o' is found in the answer.
'see' could be 'v' (short for 'vide', Latin meaning 'see elsewhere') and 'v' is present in the answer.
The remaining letters 'isr' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
'of' is the link.
Can you help me to learn more?
(Other definitions for visor that I've seen before include "Sunshade" , "Face-armour" , "Eye shield" , "Face armour" , "Peak of a cap" .)