Answer by half the people, or all of them (4)
I believe the answer is:
amen
'all of them' is the definition.
I can't tell whether this definition defines the answer.
'answer by half the people' is the wordplay.
'answer by' becomes 'a' (abbreviation eg in Q and A. I am not sure about the 'by' bit.).
'half the' indicates taking half.
'people' becomes 'bagmen' (bagman is a kind of person).
'bagmen' halved is 'men'.
'a'+'men'='AMEN'
'or' acts as a link.
Can you help me to learn more?
(Other definitions for amen that I've seen before include "statement of affirmation" , "Final word in prayer" , "Name for prayer's end" , "Prayerful last word" , "prayer's ending" .)