Left Washington institute without loyalist (8)
I believe the answer is:
stalwart
'loyalist' is the definition.
(synonyms)
'left washington institute without' is the wordplay.
'left' becomes 'l' (common abbreviation).
'washington' becomes 'wa' (abbreviation for the US state).
'institute' becomes 'start' (to institute something is to begin or start it).
'without' means one lot of letters goes inside another.
'l'+'wa'='lwa'
'lwa' going into 'start' is 'STALWART'.
(Other definitions for stalwart that I've seen before include "Resolute and firm" , "Valiant" , "Loyalist" , "husky" , "stout" .)