Opposition party missing opening of prayer (5)

I believe the answer is:

antis

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'opposition' is the definition.
(I've seen this in another clue)

I don't understand how the remainder of the clue works.

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(Other definitions for antis that I've seen before include "They're opposed to" , "They say no" , "They oppose" , "People who are opposed" , "Opponents" .)

I've seen this clue in The Times.

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