A means of communication by pipeline? (4)

I believe the answer is:

tube

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'pipeline?' is the definition.
(pipeline is a kind of tube)

I don't understand the rest of the clue.

(Other definitions for tube that I've seen before include "train network" , "channel" , "Underground transport" , "Transport system" , "TV" .)

I've seen this clue in The Irish Independent.

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