Senseless repetition and back trouble after city greeting from Barcelona (9)
I believe the answer is:
echolalia
'senseless repetition' is the definition.
(I've seen this before)
'back trouble after city greeting from barcelona' is the wordplay.
'back' shows that the letters should be reversed in order.
'trouble' becomes 'ail' (synonyms).
'after' says to put letters next to each other.
'city' becomes 'EC' (the City of London postcode).
'greeting from barcelona' becomes 'hola' (greeting in Spanish).
'ail' written backwards gives 'lia'.
'ec'+'hola'='echola'
'lia' put after 'echola' is 'ECHOLALIA'.
'and' is the link.
(Other definitions for echolalia that I've seen before include "Repetition of another's words" , "repetitive talk" , "psychiatric problem" , "Mindless repetition" , "Childish repetition of speech" .)