Style at the heart of native language (4)
I believe the answer is:
elan
'style' is the definition.
('elan' can be a synonym of 'style')
'the heart of native language' is the wordplay.
'the heart of' says the answer is hidden in the clue.
'ELAN' can be found hidden inside 'native language'.
'at' is the link.
(Other definitions for elan that I've seen before include "Snap" , "Energetic style - anagram of 3" , "Impetuosity - style" , "Vitality" , "spirit" .)