Clue vague, having lost us — answer written in which might be revealed in front (8)

I believe the answer is:

cleavage

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'clue vague having lost us answer written in which might be revealed in front' is the definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.

This is all the clue.

Can you help me to learn more?

(Other definitions for cleavage that I've seen before include "Cell division" , "Warm valley" , "Line formed by a groove between two parts" , "gap" , "Course likely to lead to bad end" .)

I've seen this clue in The Guardian.

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