"In your Easter bonnet with all the frills upon it,

"You'll be the grandest lady in the Easter parade"

Irving Berlin's song "Easter Parade" from the 1948 film "Easter Parade" with Fred Astaire and Judy Garland.

Hats show respect and honor, especially in Europe, Hester E. Oberman, who teaches psychology of religion at the UA, told the Star in 2012. Festive hats topped off the new, frilly, fancy clothes worn at Easter — a symbol of renewal — and became part of the Easter tradition.

A couple of other views: 

• Easter bonnets come from European traditions of wearing flowers on a hat to celebrate spring and developed into a way of ladies celebrating Easter, says whyeaster.com

• "Easter was once known as the 'Sunday of Joy.' After the Civil War, mothers and daughters who had donned the dark colors of mourning for such a long time began wearing colorful flowered hats and elaborate corsages as part of the Easter celebration. Their hats were adorned with blooming and fresh flowers. If the flowers were not blooming they would make them from paper, ribbon, feathers or sea shells," according to Dgreetings.com

Primary source: "April 1 is a religious holiday — gotcha, April Fools" by Peggy Fletcher Stack, The Salt Lake Tribune