Resuscitate King? Calamitous to rescuer short of oxygen (9)
I believe the answer is:
resurrect
'resuscitate' is the definition.
(resurrecting is a kind of resuscitating)
'king? calamitous to rescuer short of oxygen' is the wordplay.
'king?' becomes 'r' (r is abbreviation for rex).
'calamitous' indicates anagramming the letters.
'short of' suggests deleting specific letters.
'oxygen' becomes 'o' (atomic symbol for oxygen).
'to'+'rescuer'='torescuer'
'torescuer' with 'o' taken away is 'trescuer'.
'trescuer' is an anagram of 'esurrect'.
'r'+'esurrect'='RESURRECT'
(Other definitions for resurrect that I've seen before include "Breathe new life into" , "Raise" , "Bring back to life" , "Revive (something)" , "Revive; disinter" .)