Acclaim register, one used endlessly by Brussels (8)
I believe the answer is:
eulogise
'acclaim' is the definition.
(I've seen this before)
'register one used endlessly by brussels' is the wordplay.
'register' becomes 'log' (a log is a register).
'one' becomes 'I' (Roman numeral).
'endlessly' indicates the central letters (the ends of the words are removed).
'by' says to put letters next to each other.
'brussels' becomes 'EU' (European Parliament is based in Brussels).
The middle letters of 'used' are 'se'.
'log'+'i'+'se'='logise'
'logise' put after 'eu' is 'EULOGISE'.
(Other definitions for eulogise that I've seen before include "Praise formally and eloquently" , "Rave about" , "Laud" , "Praise highly" , "Acclaim" .)