Creature climbing across the leads? (3)
I believe the answer is:
cat
'creature' is the definition.
(thesaurus)
'climbing across the leads?' is the wordplay.
'leads?' indicates taking the first letters (I've seen 'lead' mean this).
The initial letters of 'climbing across the' is 'CAT'.
(Other definitions for cat that I've seen before include "See 21" , "Carnivore; whip" , "Feline mammel" , "Tiger, for instance" , "A tom" .)