A guest's endless complaint (4)

I believe the answer is:

ague

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'complaint' is the definition.
(ague is a kind of health problem)

'a guest's endless' is the wordplay.
'guest's endless' becomes 'gue' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'a'+'gue'='AGUE'

Can you help me to learn more?

(Other definitions for ague that I've seen before include "nasty illness?" , "attack" , "Fit of the shakes" , "Malarial fever; chill" , "Chills and fever" .)

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