Tibetans uncovered a second letter (4)

I believe the answer is:

beta

'a second letter' is the definition.
(I've seen this in another clue)

'tibetans uncovered' is the wordplay.
'uncovered' says the answer is hidden in the clue.
'BETA' is hidden in the letters of 'tibetans'.

(Other definitions for beta that I've seen before include "Second Greek letter - beat that" , "In a constellation, a star second in brightness" , "2nd letter of Greek alphabet" , "Second-rate" , "second class grade?" .)

I've seen this clue in the Sydney Morning Herald.

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