Whirling, it's pronouncedly less than steady (4)

I believe the answer is:

eddy

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But I can't explain it at all! Could you help me understand?

(Other definitions for eddy that I've seen before include "current revolution" , "Rapid circular current" , "Founder of Christian Science, d. 1910" , "Little swirl in water" , "Chap" .)

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