6 across
Manx
cat
principally
is
clearly
even
smoother
(6)
Manx cat principally is clearly even smoother (6)
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The definition is at the end of the clue.
How the clue works
Look at smoother at the end — that's your definition, something that smooths surfaces. A PUMA is a cat, and making it 'Manx' (tailless, geddit?) chops off the last letter to give you PUM. Then take the first letters ('principally') of Is Clearly Even and you get ICE, so stick the two bits together and there you have it.