Initially slippery and smooth (4)

I believe the answer is:

sand

'smooth' is the definition.
(sanding is a kind of smoothing)

'initially slippery and' is the wordplay.
'initially' suggests taking the first letters.
The first letter of 'slippery' is 's'.
's'+'and'='SAND'

(Other definitions for sand that I've seen before include "Loose grains" , "Dune constituent" , "Desert grit" , "Hourglass contents" , "Very fine grains of rock, as on beach" .)

I've seen this clue in The Sun.

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