Crossword Genius

Nature's mutated when uranium's left behind (6)

Ross

I believe the answer is:

astern

'behind' is the definition.
(at the back or behind of a ship)

I don't understand how the remainder of the clue works.

(Other definitions for astern that I've seen before include "Aft" , "Towards rear of a vessel" , "Abaft" , "Behind at sea" , "Towards a ship's rear" .)

I've seen this clue in The Guardian.
Want a hint initially instead of a full solution? Install my app