List chicken that’s lost one egg? (6)
I believe the answer is:
roster
'list' is the definition.
(a roster is a list or register)
'chicken that's lost one egg?' is the wordplay.
'chicken' becomes 'rooster' (rooster is a kind of chicken).
'that's lost' indicates named letters should be taken away (as in 'that has lost').
'one egg?' becomes 'o' (an 'o' resembles an egg).
'rooster' with 'o' taken away is 'ROSTER'.
(Other definitions for roster that I've seen before include "List of people's turn of duties" , "Duty rota" , "List showing turns of duty" , "Duty plan" , "List of duties and those who are to perform them" .)