Somnambulate (9)
I believe the answer is:
sleepwalk
'somnambulate' is the definition.
(I know that somnambulate can be written as sleepwalk)
This is the entire clue.
(Other definitions for sleepwalk that I've seen before include "promenade at night?" , "Leave bed without waking up" , "Move unconsciously?" , "Act as Lady Macbeth" , "Somnambulate" .)