For which coaches are needed to give instruction! (5)
I believe the answer is:
train
'to give instruction' is the definition.
The answer and definition can be both to do with communicating as well as being verbs in their base form.
Maybe there's an association between them I don't understand?
'for which coaches are' is the wordplay.
I cannot really understand how this works, but
'are' could be 'a' (short for 'are', historical unit of measurement) and 'a' is found within the answer.
The remaining letters 'trin' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
'needed' acts as a link.
Can you help me to learn more?
(Other definitions for train that I've seen before include "instruct and > discipline" , "Rail transport" , "Linked carriages" , "Number of eg carriages in a line" , "Long back section of a gown that's drawn along the floor" .)