Stress European parliamentarian has one son (8)
I believe the answer is:
emphasis
'stress' is the definition.
(I know that stress can be written as emphasis)
'european parliamentarian has one son' is the wordplay.
'european' becomes 'E' (abbreviation e.g. EU).
'parliamentarian' becomes 'MP' (Member of Parliament).
'one' becomes 'i' (Roman numeral).
'son' becomes 's' (genealogical abbreviation for son).
'e'+'mp'+'has'+'i'+'s'='EMPHASIS'
(Other definitions for emphasis that I've seen before include "Stress - misshape (anag)" , "Accentutation" , "Intensity of expression" , "Stress, accentuation" , "Stress laid on, eg, words" .)