Saw Chinese leader blocking American order (5)
I believe the answer is:
axiom
'saw' is the definition.
(saw can mean a saying or idea)
'chinese leader blocking american order' is the wordplay.
'chinese leader' becomes 'xi' (I can't explain this - if you can you should give a lot more credence to this answer).
'blocking' indicates putting letters inside (block can mean to plug a gap in something).
'american' becomes 'a' (common abbreviation - e.g. in organisation names).
'order' becomes 'om' (Order of Merit).
'a'+'om'='aom'
'xi' going inside 'aom' is 'AXIOM'.
Can you help me to learn more?
(Other definitions for axiom that I've seen before include "Truism - proverb" , "Self-evident principle" , "fundamental principle" , "Generally accepted principle" , "rule" .)