Character in Sophocles married sexually open-minded figures (6)
I believe the answer is:
rhombi
'figures' is the definition.
(rhombus is a kind of figure)
'character in sophocles married sexually open-minded' is the wordplay.
'character in sophocles' becomes 'rho' (letter in the Greek spelling of 'Sophocles').
'married' becomes 'm'.
'sexually open-minded' becomes 'bi' (bisexual).
'rho'+'m'+'bi'='RHOMBI'
(Other definitions for rhombi that I've seen before include "diamonds" , "Lozenge shapes" , "Four-sided figures" , "Diamond shapes (maths.)" , "certain figures in mathematics" .)