Home › Words › S › sundayismsundayismsundayism means the conservative Christian evangelism of Billy Sunday (1862–1935), American baseball player and influential evangelist.EtymologyFrom Sunday + -ism.nounThe conservative Christian evangelism of Billy Sunday (1862–1935), American baseball player and influential evangelist.A statement uttered by Billy Sunday.Definitions & examples from Wiktionary (CC BY-SA 3.0).