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 can't justify this - if you can you should believe this answer much more).
'upset' is a reversal indicator.
'coming round' indicates putting letters inside.
'with' becomes 'and'.
'droll' in reverse letter order is 'llord'.
'llord' enclosing '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" .)