the Old Bill (functioning as plural) policemen collectively or in general
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
How to use Old Bill in a sentence
Everyone stayed close in except Old Bill who was forced to drive to town for supplies and mail.
The latter had gone fishing with Old Bill as his guide, and their boat could be seen trolling slowly along the far shore.
Old Bill had been warned repeatedly to see that the boats were firmly tied, but he was careless.
Old Bill approached warily, knowing from the tone of the voice, that something unpleasant was in store.
Mr. Brownell wandered restlessly up and down the beach, watching the lake for a glimpse of the canoe or Old Bill.