English and American work at key complex (9)
I believe the answer is:
elaborate
'complex' is the definition.
(I've seen this before)
'english and american work at key' is the wordplay.
'english' becomes 'E' (abbreviation).
'and' says to put letters next to each other.
'american work' becomes 'labor' (US spelling of 'labour').
'key' becomes 'e' (a musical key).
'e'+'labor'+'at'+'e'='ELABORATE'
(Other definitions for elaborate that I've seen before include "Fussy" , "Present in further detail" , "Complicated - work out" , "Ostentatious, possibly" , "Develop in more detail" .)