It is an ingenious caption translating dialogue (8)
I believe the answer is:
subtitle
'it is an ingenious caption translating dialogue' is the definition.
The definition suggests a singular noun which matches the answer.
'it is an ingenious caption' is the wordplay.
'it is an ingenious' becomes 'sub' (I can't justify this - if you can you should believe this answer much more).
'caption' becomes 'title' (I've seen this before).
'sub'+'title'='SUBTITLE'
Can you help me to learn more?
(Other definitions for subtitle that I've seen before include "small print?" , "minor heading" , "Translation of dialogue superimposed on film" , "Translate foreign dialogue at bottom of screen" , "Explanatory legend" .)