From Gujarati tānkh artificial lake, but influenced also by Portuguese tanque, from estanque pond, from estancar to dam up,
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
Boxing slang gave us "take a dive" which lead to Tank, Tanking, i.e. to dive into the pool, or "Tank" as it was called.
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