1610s, "pool or lake for irrigation or drinking water," a word originally brought by the Portuguese from India, ultimately from Gujarati tankh
"cistern, underground reservoir for water," Marathi tanken
, or tanka
"reservoir of water, tank." Perhaps from Skt. tadaga-m
"pond, lake pool," and reinforced in later sense of "large artificial container for liquid" (1690) by Port. tanque
"reservoir," from estancar
"hold back a current of water," from V.L. *stanticare
). But others say the Port. word is the source of the Indian ones. Meaning "fuel container" is recorded from 1902. Military use originated 1915, partly as a code word, partly because they looked like benzene tanks. They were first used in action at Pozieres ridge, on the Western Front, Sept. 15, 1916. Slang meaning "detention cell" is from 1912.