A large branch providing wake-up call (5)
I believe the answer is:
alarm
'wake-up call' is the definition.
(as in an alarm clock)
'a large branch' is the wordplay.
'large' becomes 'L' (eg in clothes sizes).
'branch' becomes 'arm' (synonyms).
'a'+'l'+'arm'='ALARM'
'providing' acts as a link.
(Other definitions for alarm that I've seen before include "Panicky concern" , "Warning sound or signal" , "Noise that wakes" , "Fright" , "Daunt" .)