The Voynich Manuscript is the world’s most secretive book. It’s dated to the 15th century and contains an unknown writing system that even renowned cryptographers have never deciphered. Illustrations in the book suggest it may cover topics like herbal remedies, biology, astronomy, and the zodiac, but no one knows for sure what it really is. Source

Even more than male sodomy, sodomy between females was ‘the sin which cannot be named.’

Judith C. Brown, “Immodest Acts: The Life of a Lesbian Nun in Renaissance Italy” (pg 19). The quote continues:

“In the fifteenth century, the confessional manual attributed to Jean Gerson called it a sin against nature in which "women have each other by detestable and horrible means which should not be named or written.” In the next century, Gregario Lopez referred to it as ‘the silent sin,' peccatum mutum. For this reason Germain Colladon, the famous sixteenth century jurist, advised the Genevan authorities, who had no prior experience with lesbian crimes, that the death sentence should be read publicly, as normally was in the cases of male homosexuality, but that the customary description of the crime committed should be left out. 'A crime so horrible and against nature,’ he wrote, 'is so detestable and because of the horror of it, it cannot be named.’ The problem was not just that Colladon had a particular abhorrence for this kind of offense, but that women, because of their weaker natures, were feared to be more susceptible to suggestion. Consequently, while men found guilty of sodomy were to have their crimes read aloud in order to deter others, sexual relations between women were better left unmentioned.[emphasis added]

This speaks to why we should be wary in studying the history of sexuality about entirely relying on what public discourse says about sexuality in order to determine how all people at the time considered their sexual behaviors and the sexual behaviors of others. Furthermore, we need to be nuanced in the way we describe what terms for sexuality did or did not exist in any particular historical context. It’s not simply a matter of 'oh well a word for that just didn’t exist because nobody thought it was possible!’. Yeah…no! Often time there is so much more to it than that. There are reasons why certain terms, words, and concepts aren’t spelled out in discourse, particularly in religious discourse or in law . We need to pay mind to who formed the discourse and to what purposes they did so.

Take the religious and lawful discourse Judith C. Brown looks at here, for example. We see a refusal to name/write about women who slept with other women, but not because these particular people found the idea impossible or too confusing to articulate. Instead we see strategic silences employed in discourse about women’s sexuality as a calculated effort to control them

Catholic scholar John Gerson did not say sexuality between women could not be named. He said that it should not be named. Why? Protestant jurist Germain Colladon’s advice to Genevan authorities answers that question. Colladeen advised that authorities should not read out loud the customary description of sexual crimes committed between women (despite this being the case for sexual crimes between men) out of fear that this might inspire susceptible women.

These examples Brown examines show not a lack of understanding by people of the time concerning same-sex sexuality but in fact clear and fearful knowledge. These men understood that sexuality between women could very well happen, and felt that if they were careful they could curtail that inevitability. 

Girl With Cherries (detail); attributed to Giovanni Ambrogio de Predis (circa 1455-after 1508), but possibly by Giovanni Antonio Boltraffio (1467–1516)

oil on wood, c. 1491-5

“Girl with Cherries […] shows an artist grappling with Leonardo’s ideas and technique […] The vibrant sense of life in her curls is a testament to Leonardo’s love of the movement of hair, which he saw as similar to water currents and other paradigms of motion and which he studied in many drawings.” [source]