Decorated head of show horse with diamonds (8)
I believe the answer is:
sequined
'decorated' is the definition.
(similar in meaning)
'head of show horse with diamonds' is the wordplay.
'head of' indicates taking the first letters.
'horse' becomes 'equine' (equine means a horse or related animal).
'with' means one lot of letters go next to another.
'diamonds' becomes 'd' (abbreviation in bridge say).
The initial letter of 'show' is 's'.
's'+'equine'+'d'='SEQUINED'
(Another definition for sequined that I've seen is " Of clothes, covered with ornamental spangles".)