Awfully thin bear beginning to eat and sleep (9)
I believe the answer is:
hibernate
'sleep' is the definition.
(hibernating is a kind of sleeping)
'awfully thin bear beginning to eat' is the wordplay.
'awfully' indicates an anagram.
'beginning to' indicates taking the first letters.
The first letter of 'eat' is 'e'.
'thin'+'bear'='thinbear'
'thinbear' is an anagram of 'hibernat'.
'hibernat'+'e'='HIBERNATE'
'and' is the link.
(Other definitions for hibernate that I've seen before include "Become dormant" , "Breathe in to settle down for winter sleep" , "Breathe in for long winter sleep" , "Of animals, sleep through the winter" , "remain inactive for months" .)