Crossword Genius

Wave when tea's ready across lake? (8)

Ross

I believe the answer is:

flourish

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'wave' is the definition.
(I know that wave can be written as flourish)

I don't understand the remainder of the clue.

Can you help me to learn more?

(Other definitions for flourish that I've seen before include "Prosper - display" , "success" , "Grow vigorously and healthily" , "Wax" , "Thrive; ornamental passage of music" .)

I've seen this clue in The Telegraph.
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