Train hard by river where transport was kept? (5,5)

I believe the answer is:

coach house

I'm a little stuck... Click here to teach me more about this clue!

'where transport was kept?' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how they can define each other.

'train hard by river' is the wordplay.
'train' becomes 'coach' (synonyms).
'hard' becomes 'h' (abbreviation used in pencil classifications).
'by river' becomes 'ouse' (Yorkshire river. I am not sure about the 'by' bit.).
'coach'+'h'+'ouse'='COACH-HOUSE'

Can you help me to learn more?

(Another definition for coach house that I've seen is " Building formerly housing carriages".)

I've seen this clue in The Independent.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.