As an illustration, bromine layer coated a record (7)
I believe the answer is:
halogen
'as' is the definition.
The definition and answer can be both substances as well as being singular nouns.
Maybe they are linked in a way I don't understand?
'an illustration bromine layer coated a record' is the wordplay.
I cannot quite see how this works, but
'an' could be 'a' and 'a' is present in the answer.
'record' could be 'log' (logging is a kind of recording) and 'log' is located in the answer.
'layer' could be 'hen' (something which lays - eggs in this case) and 'hen' is located in the remaining letters.
No letters remain.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for halogen that I've seen before include "Element such as iodine" , "One of group of five elements (used in this type of lamp)" , "reactive group member" , "I must be regarded as one" , "Chlorine, fluorine, bromine, iodine or astatine?" .)