One can get cross when farewells are repeated! (5)
I believe the answer is:
adieu
'cross when farewells are repeated' is the definition.
I can't tell whether this defines the answer.
'one can' is the wordplay.
'one' becomes 'a' (a thing is one thing).
'can' becomes 'dieu' (I can't justify this - if you can you should believe this answer much more).
'a'+'dieu'='ADIEU'
'get' acts as a link.
Can you help me to learn more?
(Other definitions for adieu that I've seen before include "Leave" , "Goodbye, monsieur" , "Some say it when leaving" , "Farewell (French)" , "Vale" .)