Tea dance, 50% off (3)

I believe the answer is:

cha

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'tea' is the definition.
(cha is a type of tea)

I cannot understand how the rest of the clue works.

(Other definitions for cha that I've seen before include "Tea (informal)" , "drink" , "Rosie Lee (slang)" , "not allowed in ski lodge" , "Indian tea" .)

I've seen this clue in The Independent.

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