Crossword Genius

Shakes round top, not being this? (4-5)

Ross

I believe the answer is:

rock-solid

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'not being this?' is the definition.
I don't know anything about this answer so I can't tell whether it can be defined by this definition.

'shakes round top' is the wordplay.
'shakes' becomes 'rocks' ('rock' can be a synonym of 'shake').
'round' becomes 'o' (o is a circular letter).
'top' becomes 'lid' (lid is a kind of top).
'rocks'+'o'+'lid'='ROCK-SOLID'

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