WordNet sense 1 (as much as a tank will hold):

tankful

WordNet sense 2 (a freight car that transports liquids or gases in bulk):

tank car

WordNet sense 3 (an enclosed armored military vehicle; has a cannon and moves on caterpillar treads):

armored combat vehicle, armoured combat vehicle, army tank

WordNet sense 4 (a large (usually metallic) vessel for holding gases or liquids):

storage tank

WordNet sense 5 (a cell for violent prisoners):

cooler