Spanish line on mat for waltzer, did you say? (5)

I believe the answer is:

tilde

'spanish line' is the definition.
(accent mark used in Spanish)

I don't understand the remainder of the clue.

(Other definitions for tilde that I've seen before include "Spanish accent, as in se-or, ma-ana etc." , "Diacritical sign over letter" , "Diacritical mark over a letter thus, n" , "Augmentation of text" , "Spanish cedilla" .)

I've seen this clue in The Guardian.

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