Tube (4)
'tube' is the definition.
(pipes are tubular)
This is all the clue.
(Other definitions for pipe that I've seen before include "Hollow tube or musical instrument" , "Tube carrying liquid or gas" , "Water carrier" , "Fluid or gas transporter" , "Smoker's item" .)
'tube' is the definition.
(type of tube or canal)
This is the entire clue.
(Other definitions for duct that I've seen before include "Pipe conveying fluid or gas" , "Air passage" , "Enclosed conduit for fluid" , "Tube for cables, air, etc" , "Channel" .)
(Other definitions for boob that I've seen before include "Blunder (colloq.)" , "Mistake; breast (sl.)" , "Embarrassing mistake" , "Error" , "Slip" .)
'tube' is the definition.
(thesaurus)
This is all the clue.
(Other definitions for cylinder that I've seen before include "Piston chamber in a car" , "Tube-shaped object" , "Tube for piston" , "Long, round figure" , "Three-dimensional shape" .)
'tube' is the definition.
(inner tube is a kind of tube)
This is all the clue.
(Other definitions for inner that I've seen before include "personal" , "Annulus nearest bull" , "- - sanctum" , "(Of thoughts) intimate - (of circles) privileged" , "Private, not expressed" .)