Olympians in southeast one chained up (7)
I believe the answer is:
deities
'olympians' is the definition.
(the Olympians were ancient Greek gods or deities)
'southeast one chained up' is the wordplay.
'southeast' becomes 'SE' (synonyms).
'one' becomes 'i' (Roman numeral).
'chained' becomes 'tied' (chained or tied up).
'up' says the letters should be written backwards (in down clue: letters go upwards).
'se'+'i'+'tied'='seitied'
'seitied' written backwards gives 'DEITIES'.
'in' acts as a link.
(Another definition for deities that I've seen is " Gods and goddesses".)