Cable ultimately laid on the concrete aerial (8)
I believe the answer is:
ethereal
'aerial' is the definition.
(I know that aerial can be written as ethereal)
'cable ultimately laid on the concrete' is the wordplay.
'ultimately' indicates one should take the final letters.
'laid on' means one lot of letters go next to another.
'concrete' becomes 'real' (similar in meaning).
The final letter of 'cable' is 'e'.
'e'+'the'+'real'='ETHEREAL'
(Other definitions for ethereal that I've seen before include "Having great lightness and delicacy" , "Heavenly - fairy-like" , "'Fairy-like, delicate (8)'" , "Light, airy or spirit-like" , "Airy; heavenly" .)