Yeasayer is a noun that means someone with a positive attitude.
You may have heard of the word naysayer, a noun referring to a person constantly denying or opposing things. Conversely, a yeasayer may refer to an upbeat, positive person known for saying ‘yes’ to things. Its less flattering meaning is a person always agreeing with or being submissive to other people, as in: It makes sense that Dennis would hire a yeasayer like Chuck as his assistant. There is nothing he loves more than having someone cater to all his wishes.