Crossword Genius

An early one doesn't get trodden on! (5)

Ross

I believe the answer is:

riser

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'an early one' is the definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.

I cannot understand how the remainder of the clue works.

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(Other definitions for riser that I've seen before include "found on the staircase" , "Upright piece between steps" , "person advancing position?" , "A bit of a flight" , "Vertical piece between two steps of stairs" .)

I've seen this clue in the Evening Standard.
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