A telegram may hold back a ship (5)

I believe the answer is:

cable

I'm a little stuck... Click here to teach me more about this clue!

'a telegram' is the definition.
(cable is a kind of telegram)

I don't understand the remainder of the clue.

(Other definitions for cable that I've seen before include "Liberal Democrat" , "Telegram; wire rope" , "Anchor chain; type of TV" , "Telegraph" , "Wire; message" .)

I've seen this clue in The Globe and Mail.

Want a hint initially instead of a full solution? Install my app