/spon"sheuhn/ , n.
1. an engagement or promise, esp. one made on behalf of another.
2. Internat. Law. an engagement made on behalf of a government by an agent acting beyond his or her authority or without the required authorization and not binding on the government unless ratified.
3. the act of becoming surety for another.
[ 1670-80; sponsion- (s. of sponsio ) guarantee, equiv. to spons ( us ) (ptp. of spondere to pledge) + -ion- -ION ]