origin:  French (via medical Latin); syu-men= to sew or bind.
noun (hymenal, adjective)
1. Originally the Greek God of marriage (also Hymenaios or Hymenaeus), mentioned in many Shakespearian plays, and imbued with several origins.
In one: Hymen was a beautiful youth in love with a nobel woman whom he couldn't marry. Instead, he followed her everywhere out of devotion, going so far as to disguise himself as a woman during a "female only" ceremony.
When that group of women, including himself (in drag), and his crush, were kidnapped, Hymen eventually rallied the women to overpower their captors and return to Athens to gain freedom. Hymen struck a bargain to marry one of the captured women as a form of gratitude and thus won the hand of his beloved! Despite their different backgrounds that would've forever separated them otherwise, the marriage became one of famous happiness among citizens Thus, festivals in his honor and the association with marriage. It is said that by calling his name at a ceremony, one "invites" Hymen to attend, in order to secure a prosperous union.
2. When a baby is forming in the uterus (and everyone starts with the physical form of a female), after birth there is a left-over piece of (typically thin) membrane -- a fold of tissue -- that covers part of the entrance to a vagina, this is known as the hymen. There is no true medical purpose known, but it does protect the fetus while it is still developing in the womb, and would deter a child from accidently hurting themselves by putting anything too far into that orifice.
However, the hymen's connection to virginity is somewhat flawed, as hymens actually come in many shapes (like everything on the human body: eyes, teeth, nipples), and some hymens permit penetration without any trouble/pain/bleeding at all. It is also possible to be born without one or a hymen that so thickly covers the entrance that medical intervention is needed to assure proper evacuation of menstruation (let alone any form of penetration).
Hymens may also be torn through tampons, fingers, sex toys, and even extreme physical activity like bike-riding (though that is rare and more often an excuse used by abusers).
Then again...the hymen might not tear from any of those things.
Despite all these caveats, bleeding, or the rupture of this membrane through penetrative sexual intercourse (with a man) is still seen as a sign of virginity. And despite the interesting connection to the God of Marriage, and brides being virgins, the etymology is said to be coincidental. I don't know, I'm skeptical. But I approve of the coincidence!
End of tale: As is often the case, the female body is mysterious~ *especially to science.
Hymen (left) and Cupid (right) with the flame of love.