To have one in your tea

Around 1700, sailors began using rum to make the stale and spoilt water on long sea voyages more drinkable. The water was mixed in a ratio of 1 part rum to 4 parts water and heated, which led to the invention of grog.

Decades later, people came up with the idea of mixing tea with rum. Nowadays, the Austrian speciality Jagertee, which is made from black tea and Inländer rum, is known as a variation.

The drink is also mentioned in the song "Hoch im Norden" by German singer Udo Lindenberg - but in reverse order: "Now we'll have a rum with tea." So rum seems to be the main ingredient here...