Speak when you're spoken to (5)
I believe the answer is:
reply
'speak' is the definition.
The answer and definition can be both to do with communicating as well as being verbs in their base form.
Perhaps there's a link between them I don't understand?
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for reply that I've seen before include "Reciprocate" , "counterattack?" , "acknowledgement" , "Returned statement" , "Comeback" .)