Train to speak (7)
I believe the answer is:
express
This clue is a double definition.
'train' is the first definition.
(express is a kind of train)
'speak' is the second definition.
(I've seen this before)
'to' acts as a link.
(Other definitions for express that I've seen before include "Squeeze out - speak" , "Verbalise - train" , "Convey; high-speed" , "Rapid" , "Quickly" .)