Ordered to include large part of oar (5)
I believe the answer is:
Here is my best explanation:
'part of oar' is the definition.
('blade' is part of 'oar')
'ordered to include large' is the subsidiary indication.
'ordered' becomes 'bade' (I've seen this before).
'to include' is an insertion indicator.
'large' becomes 'l'.
'bade' placed around 'l' is 'blade'.
(Other definitions for blade that I've seen before include "Sword", "Young chap, dashing", "Runner on an ice-skate", "cutter", "Leaf, of grass, say", "Flat part of an oar", "leaf", "It has a cutting edge", "Dashing fellow" and "Knife".)