guaranty (n.)

"act or fact of guaranteeing, a being answerable for the obligations of another," 1590s, garrantye, from earlier garant "warrant that the title to a property is true" (see guarantee (n.)), with influence from Old French garantie "protection, defense; safeguard, warranty," originally past participle of garantir "to protect," from the same source. The sense of "pledge given as security" that developed 17c. in guarantee might reasonably have left the sense "act of guaranteeing" to this form of the word, but the forms remain confused.