Hennin is the name of a decorative headdress worn by women of nobility throughout Europe during the 15th century. There were several styles, all similar. The most famous of these may be the conical shaped cap, also called the steeple headdress, similar in appearance to a wizard's hat or dunce cap, often with a sheer veil draped over it. (sources at bottom)
I could find no photos or mention of an actual specimen of a hennin cap in existence today that is from the 15th century. I have read that a production issue caused many things from those years to deteriorate rather fast. Most sources reference artwork from that time as basis for research of hennin.
The horned, heart-shaped, steeple, conical, and truncated hennins seem to be the most discussed names, or types of hennin head-dresses. The styles worn for each varies greatly as can be seen in paintings and drawings.
The word hennin was first recorded as being used in reference to this type of headwear in France in 1428, but people at that time were using other names for the various headdresses that we collectively call the hennin today.
Several sources that I found state that the hennin was first seen in Europe in the early 1400s. While it's appearance was mostly modest at first, it became more decorative and even outrageous in design by the end of it's use some 70 years later. The hennin, at least the famous conical style, seems to have fallen out of fashion by the end of the century.
It is worth noting that the modern princess hat, seen in cartoons, movies, and other media, is almost certainly based on the cone shaped hennin and veil of the late medieval period in Europe. This style of hennin was worn by women of nobility and probably princesses of that time, but I have yet to see a portrait of an actual princess in one.
I gathered these sources while learning about the hennin.
This is my own personal, informal research done mostly for the benefit of my artwork. I make no claims of accuracy. I have listed sources in this bottom section for anyone who may want to read more.
Last updated 03/2021.