I saw those words in the textbook Marugoto A1. There is no explanation, just some examples of those stores (すしや、うどんや、ピザや). The ーさん ending suggest that is a person, maybe the person that cooks that ...
I have seen adjectives in both the following forms: あつみ vs あつさ しんせんみ vs しんせんさ What do these forms indicate and how do they differ? I know that the 〜さ suffix is to convert the