Bump on a toad (4)
I believe the answer is:
wart
'bump on a toad' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for wart that I've seen before include "Horny skin growth" , "Small hard growth on skin caused by virus" , "Verruca" , "Unsightly skin growth" , "Small hard viral skin blemish" .)