Lost out to Queen's horseman (6)
I believe the answer is:
ostler
'horseman' is the definition.
The answer and definition can be both people as well as being singular nouns.
Maybe there's an association between them I don't understand?
'lost out to queen's' is the wordplay.
'out' indicates anagramming the letters (out can mean wrong or inaccurate).
'to queen' becomes 'ER' (abbreviation for Elizabeth Regina).
'lost' is an anagram of 'ostl'.
'ostl'+'er'='OSTLER'
Can you help me to learn more?
(Other definitions for ostler that I've seen before include "Attendant for horses in olden times" , "He held the horse at the old inn" , "Horse minder" , "Nags for me" , "Horseman at the inn of old" .)