Seat the head of state also left (5)
I believe the answer is:
stool
'seat' is the definition.
(I know that seat can be written as stool)
'head of state also left' is the wordplay.
'head of' indicates taking the first letters.
'also' becomes 'too' (synonyms).
'left' becomes 'l' (common abbreviation).
The initial letter of 'state' is 's'.
's'+'too'+'l'='STOOL'
'the' is the link.
(Other definitions for stool that I've seen before include "Three-legged backless seat" , "Motion" , "Backless chair" , "place butt on one?" , "Simple seat" .)