Heraldic beast with very strange name (6)
I believe the answer is:
wyvern
'heraldic beast' is the definition.
(beast often used in heraldic designs)
'with very strange name' is the wordplay.
'with' becomes 'w' (abbreviation).
'strange' indicates anagramming the letters.
'name' becomes 'n' (common abbreviation e.g. on forms).
'very' is an anagram of 'yver'.
'w'+'yver'+'n'='WYVERN'
(Other definitions for wyvern that I've seen before include "Heraldic beast" , "Heraldic dragon with two legs and two wings" , "Dragon with wings in medieval heraldry" , "Winged two-legged dragon (heraldry)" , "1950s Vauxhall model" .)