To fall over him could be fatal (5)

I believe the answer is:

cliff

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'to fall over him could be fatal' is the definition.
Although both the answer and definition are singular nouns, I can't understand how they can define each other.

This is all the clue.

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(Other definitions for cliff that I've seen before include "A sheer rock-face" , "Precipice" , "-- Richard, singer" , "stony face?" , "Sir - - Richard" .)

I've seen this clue in the Evening Standard.

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