choirboy
noun
1
a novice criminal US, 1949.
2
a newly initiated member of a youth gang US, 1956.
3
a newly recruited police officer UK, 1996.
4
a prisoner who informs on others. From the sense of 'to SING' (to inform). Collected during an extensive survey of New Zealand prison slang, 1996–2000 NEW ZEALAND, 2000