Warning from leader in temple about wearing headwear (6)
I believe the answer is:
threat
'warning' is the definition.
(I know that threat is a type of warning)
'leader in temple about wearing headwear' is the wordplay.
'leader in' suggests taking the first letters.
'about' becomes 're' ('re' means regarding or about).
'wearing' indicates putting letters inside.
'headwear' becomes 'hat' (hat is a type of headwear).
The initial letter of 'temple' is 't'.
're' going within 'hat' is 'hreat'.
't'+'hreat'='THREAT'
'from' is the link.
(Other definitions for threat that I've seen before include "An intimidatory warning" , "Menace of impending evil" , "Statement of intention to harm" , "Intimidation or warning" , "Hazard" .)