Cast are able to add more detail (9)
I believe the answer is:
elaborate
'add more detail' is the definition.
'cast are able to' is the wordplay.
'cast' is an anagram indicator (letters are dispersed or cast around).
'are'+'able'+'to'='areableto'
'areableto' is an anagram of 'ELABORATE'.
(Other definitions for elaborate that I've seen before include "Fussy" , "Detailed, complicated" , "Complicated - complex" , "flesh out?" , "Very ornate or complex" .)