Have you looked up "whether" in dictionaries?
Interested in Language
It was not immediately clear whether McPherson or Tanner had attorneys.
What's the word mean underlined in red in this sentence?
You can use 'that' in that sentence, but it doesn't mean exactly the same as 'whether'. To replace 'whether', you'd have to say, "It was not immediately clear thatMcPherson or Tanner had attorneys, nor that they did not have attorneys." In this case, 'whether' means 'whether or not'.
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