Salve efferysmiller et gratus nobis tuus adventus. Hi and welcome, efferysmiller
I look up a dictionary. Sponso is a verb (I become engaged/promised to marry), promissum is a noun (a promise). Of course, "sponso" could also be ablative or dative of "sponsus". Sponsio -ionis is a noun similar to promissum.
In dictionarium inquiro. Unum verbum est, aliud nomen. Et nomen sponsi enim ablativo vel dativo casu est "sponso". Sponsio nomen promisso simile est.
I'm writing in Latin hoping for correction, and not because I'm confident in how I express myself. Latinè scribo ut ab omnibus corrigar, non quod confidenter me exprimam.