Son who cooked before daughter washed (8)
I believe the answer is:
showered
'washed' is the definition.
(showering is a type of washing)
'son who cooked before daughter' is the wordplay.
'son' becomes 's' (genealogical abbreviation for son).
'cooked' indicates an anagram (letters cooked into a new form).
'before' becomes 'ere' (poetic term for 'before').
'daughter' becomes 'd' (genealogical abbreviation).
'who' is an anagram of 'how'.
's'+'how'+'ere'+'d'='SHOWERED'
(Other definitions for showered that I've seen before include "Washed oneself in sprayed water" , "had a clean" , "Stood under a spray of water" .)