Flu? Daughter is calm (7)
I believe the answer is:
disease
'flu?' is the definition.
(flu is a kind of disease)
'daughter is calm' is the wordplay.
'daughter' becomes 'd' (genealogical abbreviation).
'calm' becomes 'ease' (ease can mean to calm).
'd'+'is'+'ease'='DISEASE'
(Other definitions for disease that I've seen before include "blight" , "Impairment of health" , "Contagion" , "affection" , "Seaside (anag) -- ailment" .)