Restless auk flew erratically (7)
I believe the answer is:
wakeful
'restless' is the definition.
(thesaurus)
'auk flew erratically' is the wordplay.
'erratically' indicates anagramming the letters.
'auk'+'flew'='aukflew'
'aukflew' with letters rearranged gives 'WAKEFUL'.
(Other definitions for wakeful that I've seen before include "Alert, vigilant" , "Not sleepy" , "Unable to sleep" , "Not getting off" .)