A guarantee or endorsement of a bill of exchange or promissory note; a signature backing a financial obligation.
From Italian or Spanish 'avallo,' from 'a-' (to) and 'valle' (valley), with obscure etymology possibly relating to feudal concepts of support. The word entered English financial terminology in the 18th century.
An aval is a fascinating medieval financial instrument that persists in modern banking—it's essentially a co-signer's guarantee, but the term is so archaic that most people now say 'endorsement' instead, not realizing they're using a more recent synonym.
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