Every single train failing to start (4)
I believe the answer is:
each
'every single' is the definition.
(I've seen this in another clue)
'train failing to start' is the wordplay.
'train' becomes 'teach' (to train someone is to instruct or teach them).
'failing to start' means to remove the first letter.
'teach' with its first letter removed is 'EACH'.
(Other definitions for each that I've seen before include "every one individually" , "Per person" , "Every one of a number" , "Ache (anag.)" , "Every - apiece" .)