TV transition saw three-D broadcast (9)
I believe the answer is:
watershed
'tv transition' is the definition.
Although both the answer and definition are singular nouns, I don't understand how one could define the other.
'saw three-d broadcast' is the wordplay.
'broadcast' indicates anagramming the letters (letters scattered or cast around).
'saw'+'three'+'d'='sawthreed'
'sawthreed' anagrammed gives 'WATERSHED'.
Can you help me to learn more?
(Other definitions for watershed that I've seen before include "dividing line" , "Turning-point in course of events, or catchment area" , "Ridge between river valleys" , "Ridge with streams on each side, a turning-point" , "Event marking a turning point" .)