Bit about old croaker (4)
I believe the answer is:
toad
'croaker' is the definition.
(I've seen this in another clue)
'bit about old' is the wordplay.
'bit' becomes 'tad' (both can mean a small amount).
'about' is an insertion indicator.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'tad' placed around 'o' is 'TOAD'.
(Other definitions for toad that I've seen before include "driver of reckless repute" , "Hall proprietor (Grahame)" , "Wind in Willows hall-owner" , "not found in Ireland" , "Tailless amphibian" .)