Complexity of speech on European research facility (11)
I believe the answer is:
elaboration
'complexity' is the definition.
(elaboration is a kind of complexity)
'speech on european research facility' is the wordplay.
'speech' becomes 'oration' (oration is a kind of speech).
'on' means one lot of letters go next to another.
'european' becomes 'E' (abbreviation e.g. EU).
'research facility' becomes 'lab' (laboratory).
'e'+'lab'='elab'
'oration' after 'elab' is 'ELABORATION'.
'of' acts as a link.
(Other definitions for elaboration that I've seen before include "Detailed development" , "Embellishment" , "Development of further detail" , "Added refinement or detail" .)