Mass of ice mostly happy daughter removed from drink (7)

I believe the answer is:

glacier

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'mass of ice' is the definition.
(I've seen this before)

I cannot understand how the rest of the clue works.

(Other definitions for glacier that I've seen before include "Flowing ice sheet" , "Slow-moving flow of ice" , "Creeping ice mass" , "River of ice" , "Mass of ice moving down a mountain" .)

I've seen this clue in The Independent.

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