noun

• (obsolete) A money changer.
• (stationery) A type of envelope with a diamond shape or V-flap that opens on the long edge.

noun

• (UK, dialect) A ditcher; a drain digger.
  "But this was no storm, the bankers could have told him. It was break of the year."
• (mining) Synonym of browman.
• (Australia, colloquial) A watercourse filled from bank to bank.

noun

• (UK, gambling) A bet that is almost certain to succeed.
• (UK, by extension) A very safe option.
  "When Jose came to Manchester United, two and a half years ago, this was the no-brainer, the banker, the one which couldn't fail. The one who had never failed."

noun

• (rail transport, British, Australia) A railway locomotive that can be attached to the rear of a train to assist it in climbing an incline.
  "Between them these engines work passenger trains on the Keith line, and also act as bankers up to Dava when required."