... gas used partly for legendarily high one? (7)
I believe the answer is:
pegasus
'one?' is the definition.
Although both the answer and definition are singular nouns, I can't understand how they can define each other.
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for pegasus that I've seen before include "group of stars" , "Winged horse of Greek myth" , "Constellation in the northern hemisphere near Andromeda and Pisces" , "Exceptional horse" , "Flier" .)