Punishment for lying in the sun? (7)

I believe the answer is:

tanning

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'lying in the sun?' is the definition.
Although both the answer and definition are present participle verbs, I cannot see how they can define each other.

I cannot understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for tanning that I've seen before include "Browning?" , "Making leather from rawhide" , "Punishing" , "hiding" , "effect of sun's rays?" .)

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

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