Horse adopted by Pathan represented fiery mixture (7)
I believe the answer is:
naphtha
'fiery mixture' is the definition.
(I've seen this before)
'horse adopted by pathan represented' is the wordplay.
'horse' becomes 'H' (abbreviation as in horse power).
'adopted by' means one lot of letters goes inside another (I've seen this in other clues).
'represented' is an anagram indicator.
'pathan' anagrammed gives 'naphta'.
'h' going into 'naphta' is 'NAPHTHA'.
(Other definitions for naphtha that I've seen before include "Solvent ingredient" , "Flammable liquid hydrocarbon mixture" , "Flammable oil from wood, coal tar, etc" , "Oil obtained from coal; hath pan (anag.)" , "fiery mixture" .)