An abbreviation or rare variant term, possibly relating to 'arbitration' or an error in transcription; not a standard dictionary word.
Likely an abbreviation or technical notation with uncertain origin; may be a misspelling or specialized jargon term.
This appears to be either a typo, an obsolete abbreviation, or specialized technical jargon that has fallen out of use—it's a good reminder that not every letter combination in a dictionary is actually a word!
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