Lewis Short
tŭbŭlus (noun M) : dim.tubus
* A small pipe or tube, a water-pipe.
* Lit., Varr. R. R. 1, 8, 4; Vitr. 8, 7; Plin. 35, 12, 46, § 159.—A smoke - pipe, Dig. 8, 2, 13.
* Transf., a bar of metal, a pig, ingot, Plin. 33, 6, 35, § 106.
Charlton T. Lewis, Charles Short, A Latin Dictionary