Good-natured female in a myth (7)
I believe the answer is:
affable
'good-natured' is the definition.
(thesaurus)
'female in a myth' is the wordplay.
'female' becomes 'f' (abbreviation).
'in' means one lot of letters goes inside another.
'myth' becomes 'fable' (I've seen this before).
'a'+'fable'='afable'
'f' inserted into 'afable' is 'AFFABLE'.
(Other definitions for affable that I've seen before include "Good-natured, sociable" , "benign" , "Courteous of pleasantly easy-going" , "Pleasant and friendly in manner" , "Amiable, genial" .)