Elevated part of heel-bone is impressive (5)
I believe the answer is:
noble
'impressive' is the definition.
('noble' can be similar in meaning to 'impressive')
'elevated part of heel-bone' is the wordplay.
'elevated' is a reversal indicator.
'part of' indicates the answer is hidden within the clue.
'elbon' can be found hidden inside 'heel bone'.
'elbon' back-to-front is 'NOBLE'.
'is' is the link.
(Other definitions for noble that I've seen before include "titled person" , "Titled peer of the realm" , "Magnificent old coin" , "Illustrious, peer" , "August" .)