Jack released from harm displays temper (5)
I believe the answer is:
inure
'temper' is the definition.
(I've seen this before)
'jack released from harm' is the wordplay.
'jack' becomes 'J' (playing card abbreviation).
'released from' suggests deleting specific letters.
'harm' becomes 'injure' (I've seen this in another clue).
'injure' with 'j' taken away is 'INURE'.
'displays' is the link.
(Other definitions for inure that I've seen before include "Harden, make accustomed to" , "Harden or accustom as to something unpleasant" , "To give experience" , "Steel" , "Harden against, make tough" .)