Biggish bird that was duck kept by old woman (3)
I believe the answer is:
moa
'biggish bird' is the definition.
'moa' can be an answer for 'bird' (extinct flightless bird of New Zealand). I am not sure about the 'biggish' bit.
'duck kept by old woman' is the wordplay.
'duck' becomes 'o' (resembles zero - 'duck' in cricket).
'kept by' indicates putting letters inside.
'old woman' becomes 'ma' (both can mean someone's mother).
'o' inserted into 'ma' is 'MOA'.
'that was' is the link.
Can you help me to learn more?
(Other definitions for moa that I've seen before include "bird that became extinct" , "Extinct flightless bird of New Zealand" , "Old bird" , "was hunted by Maori" , "Bird no longer" .)