Pin-up may cut hot stuff (5)

I believe the answer is:

magma

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'hot stuff' is the definition.
(molten rock)

'pin-up may cut' is the wordplay.
'pin up' becomes 'mag' (I can't explain this - if you can you should believe this answer much more).
'cut' means to remove the last letter.
'may' with its final letter removed is 'ma'.
'mag'+'ma'='MAGMA'

Can you help me to learn more?

(Other definitions for magma that I've seen before include "Lava" , "That's hot!" , "hot stuff" , "Hot molten rock" , "Hot fluid rock" .)

I've seen this clue in The Daily Express.

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