There are multiple definitions - click on the translation that matches your context.

avalist

substantiv

full

endorser

noun

Definitions of endorser

English

someone who endorses a bill, cheque, or other negotiable instrument (=to sign a cheque, bill of exchange or other negotiable instrument to make it payable to another person or cashable by any person)

Every endorser and guarantor of this Note hereby assents to any extension or postponement of the time of payment.