One with a crush on you won't poison you (5)

I believe the answer is:

snake

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'one' is the definition.
Although both the answer and definition are singular nouns, I don't understand how they can define each other.

I don't understand the remainder of the clue.

Can you help me to learn more?

(Other definitions for snake that I've seen before include "Entertainer with music and reptiles" , "Wind" , "Move sinuously" , "former EC currency band" , "Asp, perhaps?" .)

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