Horse in stable needed by one riding (8)
I believe the answer is:
stallion
'horse' is the definition.
(thesaurus)
'stable needed by one riding' is the wordplay.
'stable' becomes 'stall' (I've seen this in other clues).
'needed by' says to put letters next to each other.
'one' becomes 'i' (Roman numeral).
'riding' becomes 'on' (I've seen this in other clues).
'stall'+'i'+'on'='STALLION'
'in' is the link.
(Other definitions for stallion that I've seen before include "Stud" , "Uncastrated adult male horse" , "Male horse, often used for breeding" , "Mare's mate" , "Male steed" .)