Senior citizen’s boarding-house on European river (9)
I believe the answer is:
pensioner
'senior citizen's' is the definition.
(I've seen this before)
'boarding-house on european river' is the wordplay.
'boarding house' becomes 'pension' (I've seen this before).
'on' means one lot of letters go next to another.
'european river' becomes 'er' (this could be a standard abbreviation which I don't know about).
'pension'+'er'='PENSIONER'
Can you help me to learn more?
(Other definitions for pensioner that I've seen before include "senior citizen" , "retiree" , "Retired person" , "Maybe Chelsea man" , "Former worker" .)