Meaning

noun conduit consisting of a long hollow object (usually cylindrical) used to hold and conduct objects or liquids or gases

noun electronic device consisting of a system of electrodes arranged in an evacuated glass or metal envelope

noun a hollow cylindrical shape

originFrom Middle French tube, from Latin tubus (“tube, pipe”), related to tuba (“long trumpet; war-trumpet”), of obscure ultimate origin, but possibly connected to tībia (“shinbone, reed-pipe”); see there. Doublet of tubus.

Etymology from Wiktionary, CC BY-SA 3.0