Rare panic involving head of chambers (6)
I believe the answer is:
scarce
'rare' is the definition.
('scarce' can be similar in meaning to 'rare')
'panic involving head of chambers' is the wordplay.
'panic' becomes 'scare' ('scare' can be a synonym of 'panic'**).
'involving' means one lot of letters goes inside another.
'head of' says to take the initial letters.
The first letter of 'chambers' is 'c'.
'scare' going around 'c' is 'SCARCE'.
(Other definitions for scarce that I've seen before include "exceptional" , "Deficient in quantity" , "Rarely found" , "Not enough to satisfy demand" , "Hard to obtain" .)