Bird starts to ingest big insect slowly (4)
I believe the answer is:
ibis
'bird' is the definition.
(ibis is a kind of bird)
'starts to ingest big insect slowly' is the wordplay.
'starts to' says to take the initial letters.
The initial letters of 'ingest big insect slowly' is 'IBIS'.
(Other definitions for ibis that I've seen before include "Wader with a long down-curved bill" , "Wading bird sacred to the Egyptians" , "Revered bird" , "Glossy wading bird" , "Wader worshipped by ancient Egyptians" .)