Breathe in (anag) – to become dormant (9)
![Ross](/clue/static/ross-mug.min.png)
I believe the answer is:
hibernate
(Other definitions for hibernate that I've seen before include "remain inactive for months" , "Breathe in to settle down for winter sleep" , "go out in the snow?" , "Pass the winter in a dormant state" , "Sleep durning winter" .)