It's hard to say without more context. It's a slightly odd phrase. My guess is that it means 'go down a diagonal quickly'.
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Because of Whit
In Diagram 78, the White ?anchettoed Bishop on g2 is clearly superior to the Black Bishop on d7. With his bishop searing dawn the h1—a8 diagonal, White threatens to penetrate B1ack's position with Ra8. Another threat is 1.Rd1, by which White pins the Black Bishop on d7 and wins it. In the diagram. it is Black‘s move.