Eccentric upset, coming round with letter (8)
I believe the answer is:
landlord
'letter' is the definition.
(I've seen this before)
'eccentric upset coming round with' is the wordplay.
'eccentric' becomes 'droll' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'upset' says the letters should be written backwards.
'coming round' is an insertion indicator.
'with' becomes 'and'.
'droll' in reverse letter order is 'llord'.
'llord' going around 'and' is 'LANDLORD'.
Can you help me to learn more?
(Other definitions for landlord that I've seen before include "Pub manager" , "Innkeeper" , "Mein host" , "One leasing property" , "He owns the building, collects the rent" .)