Mad reason for a drawer of trains (10)
I believe the answer is:
locomotive
'a drawer of trains' is the definition.
I can't tell whether this defines the answer.
'mad reason' is the wordplay.
'mad' becomes 'loco' (I've seen this in another clue).
'reason' becomes 'motive' (I've seen this before).
'loco'+'motive'='LOCOMOTIVE'
'for' is the link.
Can you help me to learn more?
(Other definitions for locomotive that I've seen before include "Rocket, perhaps" , "Railway engine" , "for moving from place to place" , "one's attached to the train" , "Able to move by oneself" .)