Animal showing excessive hesitation (5)
I believe the answer is:
otter
'animal' is the definition.
(thesaurus)
'excessive hesitation' is the wordplay.
'excessive' becomes 'ott' (short for 'over the top' - informal British).
'hesitation' becomes 'er'.
'ott'+'er'='OTTER'
'showing' acts as a link.
(Other definitions for otter that I've seen before include "Tarka, for one" , "bad-tempered little beast" , "one that eats fish" , "Water-loving animal" , "Water creature" .)