Definition of boron trifluoride
: a colorless pungent gas BF3 that fumes in moist air, that is made usually by reaction of a boron compound (such as borax) with a fluoride (such as hydrogen fluoride) and then sulfuric acid, and that is used chiefly as an acidic catalyst in organic reactions (such as alkylations and polymerizations)
a sum of money that is sent as a payment
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