Stocky Greek character's around to protect queen (5)
I believe the answer is:
squat
'stocky' is the definition.
(synonyms)
'greek character's around to protect queen' is the wordplay.
'greek character's' becomes 'taus' (letter from the Greek alphabet).
'around' says the letters should be written in reverse.
'to protect' indicates putting letters inside (inserted letters are held or protected).
'queen' becomes 'Q' (abbreviation for queen in chess).
'taus' in reverse letter order is 'suat'.
'suat' placed around 'q' is 'SQUAT'.
(Other definitions for squat that I've seen before include "building taken over" , "Short exercise" , "Compact" , "Illegal occupation of building" , "Crouch - occupy a property" .)