Lines etched in a mostly indifferent representation of the sun (6)
I believe the answer is:
apollo
'the sun' is the definition.
(thesaurus)
'lines etched in a mostly indifferent representation of' is the wordplay.
I cannot really see how this works, but
'lines' could be 'll' (I've seen this in other clues) and 'll' is found within the answer.
'a' is present in the answer.
'of' could be 'o' and 'o' is located in the answer.
The remaining letters 'po' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for apollo that I've seen before include "Fair youth" , "handsome fellow" , "Deity" , "Greek god (twin brother of Artemis)" , "Greek god; large European butterfly" .)