Trace long line (4)

I believe the answer is:

dash

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This might be a double definition.

'trace long' is the first definition.
'dash' can be an answer for 'trace' (thesaurus). I'm not certain of the 'long' bit.

'line' is the second definition.
(thesaurus)

Can you help me to learn more?

(Other definitions for dash that I've seen before include "Short line; run" , "Run; lan" , "Hyphen - bother!" , "Hurry ("must ____!")" , "Dart" .)

I've seen this clue in The Telegraph.

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