old soldier

plural old soldiers

1. alsofigurativelyA former soldier, or one who has served for a long time.First known use 17th c.

   For almost 90 years, the dependable 350hp diesel-electrics and their predecessors have given loyal service to Britain's industrial and main line railways, but even these old soldiers can't go on forever.

   2022 February 9, Ben Jones, “Batteries included for future shunters”, in RAIL, number 950, page 54

2. Someone with a lot of experience in something; an old hand.First known use 18th c.
3. USslangThe butt of a smoked cigar, or an empty bottle of liquor.First known use 19th c.
4. slangA bottle whose contents are drunk at a single sitting.