He made a dead set at her. A pointed or decided determination to bring matters to a crisis. The allusion is to a setter dogthat has discovered game, and makes a dead set at it.
To be at a dead set is to be set fast, so as not to be able to move. The allusion is to machinery.
To make a dead set upon someone is to attack him resolutely, to set upon him; the allusion being to dogs, bulls, etc., set on each other to fight.
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