Twiddles one's thumbs (5)
I believe the answer is:
idles
'twiddles one's thumbs' is the definition.
('idle' can be a synonym of 'twiddle one's thumbs')
This is the entire clue.
(Other definitions for idles that I've seen before include "Lazes around" , "Lazes about, just ticks over" , "Of engine, just ticks over in neutral" , "Spends time doing nothing" , "Wastes time" .)