Small amount of exuberance, head being absent (5)
I believe the answer is:
ounce
'small amount' is the definition.
(an ounce is a small amount)
'exuberance head being absent' is the wordplay.
'exuberance' becomes 'bounce' (bounce can mean exuberance or vigour).
'head being absent' means to remove the first letter.
'bounce' with its first letter taken away is 'OUNCE'.
'of' is the link.
(Other definitions for ounce that I've seen before include "Small unit of weight" , "Approx. twenty-eight gm" , "Small quantity - snow leopard" , "Carnivore" , "weight? Surely not" .)