Sibling (6)
'sibling' is the definition.
(female sibling)
This is all the clue.
(Other definitions for sister that I've seen before include "Relative in hospital?" , "Female relation" , "'Nurse, nun or relative (6)'" , "Resits (anag.)" , "Nurse, nun and sibling" .)
'sibling' is the definition.
(male sibling)
This is the entire clue.
(Other definitions for brother that I've seen before include "Male sibling" , "Relation" , "Union member - male relative" , "Trade unionist" , "Eg, monk, friar" .)