Abundance of work in CIA supporting company run badly (10)
I believe the answer is:
cornucopia
'abundance' is the definition.
(cornucopia is a kind of abundance)
'work in cia supporting company run badly' is the wordplay.
'work' becomes 'op' (abbreviation for opus).
'in' is an insertion indicator.
'supporting' is a charade indicator (letters next to each other) (in a down clue, some letters go below others).
'company' becomes 'co' (abbreviation).
'badly' indicates an anagram.
'op' inserted within 'cia' is 'copia'.
'run' anagrammed gives 'rnu'.
'co'+'rnu'='cornu'
'copia' after 'cornu' is 'CORNUCOPIA'.
'of' acts as a link.
(Other definitions for cornucopia that I've seen before include "Abundant supply of good things" , "Symbol of plenty" , "Wealth" , "There's plenty here!" , "mine" .)