Be a drifter? (5)

I believe the answer is:

float

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'be a drifter?' is the definition.
Although both the answer and definition are singular nouns, I cannot see how one could define the other.

This is the entire clue.

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(Other definitions for float that I've seen before include "Be buoyant" , "Bob" , "Lie on surface of water" , "Stay on the surface without sinking" , "Petty cash - milk vehicle - fishing aid" .)

I've seen this clue in the Evening Standard.

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