Pulsating (9)
(Other definitions for vibrant that I've seen before include "Vivacious" , "Bright, thrilling or resonant" , "Lively; pulsating" , "Dynamic" , "Aquiver with life and excitement" .)
'pulsating' is the definition.
('throb' can be a synonym of 'pulsate')
This is all the clue.
(Other definitions for throbbing that I've seen before include "Beating" , "Pulsating" .)