Meaning

noun an enclosed armored military vehicle; has a cannon and moves on caterpillar treads

noun a large (usually metallic) vessel for holding gases or liquids

noun as much as a tank will hold

originFrom Portuguese tanque (“tank, liquid container”), from an Indo-Aryan language, likely Gujarati ટાંકી (ṭā̃kī, “cistern”) or Marathi टांकी (ṭāṅkī). Compare the Arabic verb اِسْتَنْقَعَ (istanqaʕa, “to become stagnant, to stagnate”). First attested in the 1610s. * In the sense of armoured vehicle, prototypes were described as tanks for carrying water to disguise their nature and due to physical…

Etymology from Wiktionary, CC BY-SA 3.0