Supposed, we hear, hotel by Yorkshire river is a small one (10)

'a small one' is the definition.
Although both the answer and definition are singular nouns, I can't understand how one could define the other.

'supposed we hear hotel by yorkshire river' is the wordplay.
'supposed' becomes 'guessed' ('guess' can be a synonym of 'suppose').
'we hear' shows a homophone (sound like).
'hotel by' becomes 'h' (I am not sure about this - if you are sure you should believe this answer much more).
'yorkshire river' becomes 'ouse' (the Ouse is a river in Yorkshire).
'guessed' sounds like 'guest'.
'guest'+'h'+'ouse'='GUESTHOUSE'

'is' is the link.

Can you help me to learn more?