Woman, one associated with Descartes? (5)
I believe the answer is:
irene
'woman' is the definition.
(I've seen this before)
'one associated with descartes?' is the wordplay.
'one' becomes 'i' (Roman numeral).
'associated with' says to put letters next to each other.
'descartes?' becomes 'rene' ('Rene Descartes' can be a synonym of 'descartes').
'i'+'rene'='IRENE'
(Other definitions for irene that I've seen before include "Girl's name; Soames Forsyte's first wife" , "US actress, -- Dunne" , "Goddess of peace - Byzantine ruler" , "In Greek mythology, the goddess of peace" , "Girl of peace" .)