Holy Father doesn't get half the speculation (6)

I believe the answer is:

theory

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'speculation' is the definition.
(thesaurus)

I don't understand the remainder of the clue.

(Other definitions for theory that I've seen before include "Supposition intended to explain observations" , "Idea to explain something, say evolution" , "Hypothesis or concept" , "can provide an explanation" , "Idea for testing" .)

I've seen this clue in the Irish Times.

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