Wants to be slow, cycling (5)

I believe the answer is:

lacks

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'wants' is the definition.
('lack' can be a synonym of 'want')

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for lacks that I've seen before include "Needs" , "Doesn't have" , "Wants, is deficient in" , "Has a want" , "Is without, wants" .)

I've seen this clue in The Telegraph.

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