WATER TANK SUPPLY UNITS

The word tank in reference to the armored fighting vehicles is unsurprisingly predated by the word tank meaning "large receptacle," but the story connecting them is rather interesting. When the armored tank was invented in 1915, it was provisionally described as a "Caterpillar Machine Gun Destroyer" or "Land Cruiser," but defense officials in the United Kingdom were concerned about the name being leaked to enemy intelligence, so, for secrecy's sake, they were labelled as "Water Tank Supply Units", which was shortened to "tank" because it rolled off the tongue better. The word for "receptacle" came to English in the mid-seventeenth century through Portuguese tanque, which referred to any kind of "liquid container." That was most likely picked up by traders from either the Gujarati word tankh or the Marathi word tanka, both meaning "cistern" or "reservoir." Finally it probably all traces back to the Sanskrit word tadaga-m, meaning "pool," but is also a small faction of linguists who think that the Indian words actually come from tanque, and the Portuguese word is actually from Latin stagnum​, meaning "pool" as well.