Particular motor fuel developed (7)
I believe the answer is:
careful
'particular' is the definition.
(thesaurus)
'motor fuel developed' is the wordplay.
'motor' becomes 'car' (I've seen this before).
'developed' indicates anagramming the letters.
'fuel' anagrammed gives 'eful'.
'car'+'eful'='CAREFUL'
(Other definitions for careful that I've seen before include "Watch it!" , "Guarded" , "Thrifty" , "Attentive" , "Diligent" .)