Grand female relative skinny (5)
I believe the answer is:
gaunt
'skinny' is the definition.
(thesaurus)
'grand female relative' is the wordplay.
'grand' becomes 'G' (G is short for ground as in a thousand).
'female relative' becomes 'aunt' (I've seen this before).
'g'+'aunt'='GAUNT'
(Other definitions for gaunt that I've seen before include "Hence John" , "Very slight" , "Drawn" , "Grim" , "Thin or emaciated" .)