Wide of the mark describing flat object (6)
I believe the answer is:
astray
'wide of the mark' is the definition.
(I've seen this before)
'flat object' is the wordplay.
I cannot quite understand how this works, but
'object' could be 'ra' (Ra is an example) and 'ra' is located in the answer.
This explanation may well be incorrect...
'describing' is the link.
Can you help me to learn more?
(Other definitions for astray that I've seen before include "Wandering lost" , "In a lost state" , "Adrift - misguided - lost" , "Missing, lost" , "Like carrier" .)