Expressive European mass interrupted by heartless queen (8)
I believe the answer is:
eloquent
'expressive' is the definition.
(eloquent means expressive or articulate)
'european mass interrupted by heartless queen' is the wordplay.
'european' becomes 'e' (abbreviation e.g. EU).
'mass' becomes 'lot' (synonyms).
'interrupted by' indicates putting letters inside.
'heartless' says to hollow out the word (remove centre letters).
'queen' with its middle removed is 'quen'.
'lot' placed around 'quen' is 'loquent'.
'e'+'loquent'='ELOQUENT'
(Other definitions for eloquent that I've seen before include "Well-spoken - articulate" , "Speaking powerfully" , "Fluent in language" , "Verbally fluent and persuasive" , "Well-expressed" .)