Notice one organisation we have left getting the last word (5)
I believe the answer is:
adieu
'the last word' is the definition.
(I've seen this in another clue)
'notice one organisation we have left' is the wordplay.
I cannot really understand how this works, but
'notice' could be 'ad' (short for advert) and 'ad' is located in the answer.
'one' could be 'i' (Roman numeral) and 'i' is located in the answer.
This may be the basis of the clue (or it may be nonsense).
'getting' acts as a link.
Can you help me to learn more?
(Other definitions for adieu that I've seen before include "12 Down" , "Farewel" , "Parting greeting" , "Some say it when leaving" , "Farewell to France" .)