Seriously back heartless lady (7)
I believe the answer is:
sternly
'seriously' is the definition.
Both the answer and definition are adverbs. Maybe they are linked in a way I don't understand?
'back heartless lady' is the wordplay.
'back' becomes 'stern' (stern is a kind of back).
'heartless' suggests removing the centre.
'lady' with its centre taken out is 'ly'.
'stern'+'ly'='STERNLY'
Can you help me to learn more?
(Other definitions for sternly that I've seen before include "In serious way" , "Cruelly" .)