Some luminosity is able to lead astray (7)
I believe the answer is:
candela
'some luminosity' is the definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.
'able to lead astray' is the wordplay.
'able' becomes 'can'.
'to' means one lot of letters go next to another.
'astray' indicates an anagram.
'lead' anagrammed gives 'dela'.
'can'+'dela'='CANDELA'
'is' is the link.
Can you help me to learn more?
(Other definitions for candela that I've seen before include "measure of light" , "Unit of luminous intensity" , "Measure of brilliance" .)