There's something fragrant about London's city still (6)
I believe the answer is:
becalm
'still' is the definition.
(thesaurus)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for becalm that I've seen before include "Keep motionless by lack of wind" , "Leave (sailing ship) without wind" , "Leave a sailing vessel unable to move for lack of wind" , "Make quiet or still - sounds like an order" , "Make quiet or still - that's an order?" .)