Seat adds diesel development (4-6)
I believe the answer is:
side-saddle
'seat adds diesel development' is the definition.
I can't tell whether this defines the answer.
'adds diesel development' is the wordplay.
'development' is an anagram indicator.
'adds'+'diesel'='addsdiesel'
'addsdiesel' is an anagram of 'SIDE-SADDLE'.
Can you help me to learn more?
(Other definitions for side-saddle that I've seen before include "Sitting like a woman rider" , "Way of riding a horse" , "On horse as some riders" , "Not astride" , "Style of riding" .)