as good as, commensurate, equal, equivalent, synonymous, the same as
English Collins Dictionary - English synonyms & Thesaurus
If you say that one thing is tantamount to a second, more serious thing, you are emphasizing how bad, unacceptable, or unfortunate the first thing is by comparing it to the second.
FORMAL adj v-link ADJ to n/-ing (emphasis)
What Bracey is saying is tantamount to heresy...
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