Let's say it was new in 1984 (5)
I believe the answer is:
speak
'let's say' is the definition.
'speak' can be an answer for 'say' (synonyms). I'm not sure about the 'let's' bit.
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for speak that I've seen before include "Orate" , "Converse" , "Utter words" , "express" , "Talk" .)