Tyrant from regimental HQ receiving head of state (6)
I believe the answer is:
despot
'tyrant' is the definition.
(I know that tyrant can be written as despot)
'regimental hq receiving head of state' is the wordplay.
'regimental hq' becomes 'depot' (headquarters).
'receiving' means one lot of letters goes inside another.
'head of' suggests taking the first letters.
The first letter of 'state' is 's'.
'depot' enclosing 's' is 'DESPOT'.
'from' is the link.
(Other definitions for despot that I've seen before include "Gaddafi, say" , "Arbitrary ruler" , "Person with more than enough power" , "Louis XVI was one" , "Tyrant, slave driver" .)