Eg Clydesdale press first to show revolutionary engine (4,5)
I believe the answer is:
iron horse
'revolutionary engine' is the definition.
(supposed Native American term for a locomotive)
'eg clydesdale press first' is the wordplay.
'eg clydesdale' becomes 'horse' (type of horse).
'press' becomes 'iron' (ironing is a kind of pressing).
'first' is a charade indicator (letters next to each other).
'horse' after 'iron' is 'IRON HORSE'.
'to show' is the link.
(Other definitions for iron horse that I've seen before include "Old name for locomotive" , "worn-out engine" , "An invention of the steam age" , "Train leader" , "loco" .)