have something on good authority
from good hands
confirmatively
straight from the horse's mouth
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plausibly
confirmably
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corroboration
provably
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vouch
confirmation
substantiation
right as rain
verification
authority
attestedly
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ascertainably
factuality
ascertainable
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ascertainedly
likely
prima facie
probably
belike
in all likelihood
in all probability
confirmatorily
positive statement
overprecise
straight
factiously
fountainhead
fact check
factically
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factually
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cogent
intersource
provenanced
how
semiproven
datum
supported
certain