Makes harder to fathom? (7)

I believe the answer is:

deepens

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'makes' is the definition.
The answer and definition can be both related to change as well as being verbs in their -s form.
Perhaps you can see a link between them that I can't see?

I can't explain the remainder of the clue.

Can you help me to learn more?

(Other definitions for deepens that I've seen before include "Dredges" , "Intensifies" , "increases" , "gets stronger" , "Make further down, say ditch" .)

I've seen this clue in The Globe and Mail.

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