Section of the lung’s damaged — avoid snuff essentially (6)

I believe the answer is:

length

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'section' is the definition.

I can't explain the remainder of the clue.

(Other definitions for length that I've seen before include "Linear dimension" , "End-to-end dimension" , "Extensiveness - measure" , "A bit of swimming" , "Measurement from end to end" .)

I've seen this clue in The Hindu.

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