Blockage I end in diplomatic reasoning (5)
I believe the answer is:
logic
'reasoning' is the definition.
(I've seen this in another clue)
'blockage i end in diplomatic' is the wordplay.
'blockage' becomes 'log' (I can't justify this - if you can you should give a lot more credence to this answer).
'end in' suggests the final letters.
The last letter of 'diplomatic' is 'c'.
'log'+'i'+'c'='LOGIC'
Can you help me to learn more?
(Other definitions for logic that I've seen before include "Reasoned argument" , "method of reasoning" , "Rationale ?" , "this makes sense" , "System of reasoning" .)