Skill in pursuit of express plane (8)
I believe the answer is:
aircraft
'plane' is the definition.
(I've seen this before)
'skill in pursuit of express' is the wordplay.
'skill' becomes 'craft' (craft is a kind of skill).
'in pursuit of' says to put letters next to each other (some letters chase after others).
'express' becomes 'air' (I've seen this before).
'craft' after 'air' is 'AIRCRAFT'.
(Other definitions for aircraft that I've seen before include "I cart RAF? (Anag)" , "Airbus A380 or Boeing 777, say" , "High-flier" , "Flying machines" , "Eg, seven four seven or Airbus" .)