What is the meaning of ー・

Question

Can someone tell me what the notation "ー・" means?

It's all over this article: 大辞林「いう【言う・云う・謂う】」

Answer 1

It simply means that it should be replaced by 言, 云 or 謂 in actual usage.

The notation is used exclusively in some dictionaries to avoid looking repetitive in giving example phrases/sentences for the entry word.

(Of course, one could argue that the use of the same notation over and over looks repetitive, too.)

Answer 2

This dictionary definition, which you quoted, looks a bit half-baked.

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Have a look at 大辞泉 for 話す.

It first defines the root (constant) part:

はな・す

And then uses it in examples:

「電話で―・す」

「父に―・してから返事する」

Where the part before the dot is constant and the ending is conjugated/inflected.

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Back to the example from the question, it should define い・う for the examples to make sense.