Vital icicles have slanted interior (6)

I believe the answer is:

italic

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'slanted interior' is the definition.
'italic' can be an answer for 'slanted' (I've seen this in another clue). I am unsure of the 'interior' bit.

'vital icicles have' is the wordplay.
'have' indicates the answer is hidden within the clue.
'ITALIC' is hidden within 'vital icicles'.

Can you help me to learn more?

(Other definitions for italic that I've seen before include "Sloping script" , "Kind of typeface" , "not exactly an upright type" , "kind of signing" , "Inclined to emphasise" .)

I've seen this clue in The Daily Express.

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