Grand bird, traditionally quested for (5)
I believe the answer is:
grail
'traditionally quested for' is the definition.
I can't tell whether this definition defines the answer.
'grand bird' is the wordplay.
'grand' becomes 'g' (G is short for ground as in a thousand).
'bird' becomes 'rail' (a wading bird).
'g'+'rail'='GRAIL'
Can you help me to learn more?
(Other definitions for grail that I've seen before include "Holy vessel used at the Last Supper" , "Famous chalice" , "sought by Parsifal" , "Round Table Knights sought the Holy ....." , "Fabled holy vessel" .)