King with deformed ear, seldom seen (4)
I believe the answer is:
rare
'seldom seen' is the definition.
(thesaurus)
'king with deformed ear' is the wordplay.
'king' becomes 'r' (r is abbreviation for rex).
'with' is a charade indicator (letters next to each other).
'deformed' is an anagram indicator.
'ear' with letters rearranged gives 'are'.
'r'+'are'='RARE'
(Other definitions for rare that I've seen before include "Scarcely seen" , "Rear up, being scarce" , "Very infrequent or scarce" , "difficult to find?" , "'Unusual, uncommon (4)'" .)