This morning I'm rereading parts of Othello (for a theater review I'm supposed to be writing right now) and just stumbled over one of its final lines, which Lodovico shouts at the depth of the play's horror, when everybody else is dead or almost-dead:

O bloody period!

That line is notorious for cracking up high schoolers during student matinees—I remember my sophomore English class cracking up at that when we were reading it aloud—but for how many generations? When did "period" (from the Greek periodos, literally peri- "around" and hodos "a going, way, journey") become synonymous with "menstruation"?

According to the Oxford English Dictionary*, that usage first appeared in 19th-century medical books. From 1822: "The exact day between any two periods of menstruation in which semination has taken effect." It's used as a more explicit synonym in 1879: "Her habit is for the periods to recur every five weeks, rather freely." And it turns up in an advertisement from 1891 hawking "Ladies' 'Period' Towels."

American students have definitely been reading Shakespeare since then—years ago, my grandfather gave me a leather-bound book of Shakespeare plays from around that time that his great-uncle (or somebody) read in high school. (Whoever it was wrote notes in pencil in a shaky, adolescent scrawl—and the first few pages, made of onionskin, are torn out. Granddad said that when he was a kid he'd ripped them out to use a rolling papers.)

So Shakespeare's "O bloody period!" has probably been making students snicker for around 150 years, or six generations. In case you were wondering.

*The definition of "period" as "menstruation" in the OED is 3b., a subset of definition 3, which is "the time during which a disease runs its course... each of the temporal phases distinguishable in the course of a disease." Technically, period-as-menstruation is classified a subset of period-as-disease, which speaks volumes about gender and medicine.

And "menstruation" comes from the Latin menstruus, or "monthly." Old English had a similar word, monaðblot, or "month-blood."