Not able to be ascribed or attributed to a particular source(adjective)
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Use "unattributable" in a sentence
""I hope that by my record I've shown that I can deliver and I want the people of Wales to judge me on my record, not on these kind of unattributable briefings which obviously would undermine things otherwise.""
"Since its creation, the STL, as it's known, has not indicted a single suspect (although it released four), and there have only been rumblings about what conclusions it will draw (gleaned from unattributable leaks)."
""To leak is one of the irregular verbs; I make unattributable briefings, you leak, he is charged under Section 30 of the Offical Secrets Act.""