Austen heroine reflected on German dowager's stern measure (6)
I believe the answer is:
gramme
'measure' is the definition.
(gramme is a kind of measure)
'austen heroine reflected on german dowager's stern' is the wordplay.
'austen heroine' becomes 'Emma' (heroine of Jane Austen's novel Emma).
'reflected' is a reversal indicator (letters reflected back).
'on' says to put letters next to each other.
'german dowager's stern' becomes 'gr' (I can't justify this - if you can you should give a lot more credence to this answer).
'emma' back-to-front is 'amme'.
'amme' after 'gr' is 'GRAMME'.
Can you help me to learn more?
(Other definitions for gramme that I've seen before include "Small weight" , "Arm Meg (anag)" , "One thousandth of a kilogram (Fr)" , "Small unit of mass" , "Metric unit of weight" .)