Last weekend I got a card for our new local library and borrowed a book about language and the DVDs for the tv science-fiction series Firefly, which I have read small amounts about over the years but never seen. The series mixes futuristic science fiction with wild west settings, as the outer planets and moons of a complex solar system (or an inter-related group of solar systems; it isn’t fully explained) were terraformed to a basic level but the settlers are otherwise expected to fend for themselves.
In one episode the lead character unexpectedly finds himself married by local custom to a young woman who may or may not be what she seems (semi-spoiler: she isn’t). At one point she refers to “my sistren” in “the maiden house”.
Sistren is a real English word, but is not in general use like brethren. In the past, more English plurals were formed by adding –en, of which children is by far the most common. (See Wikipedia.) Dictionary.com and the Oxford Living Dictionaries do not record it. Merriam-Webster defines it as “chiefly dialectal plural of SISTER”. Sistren and brethren started as the ordinary plurals of sister and brother, but were overtaken by the regular sisters and brothers, and came to be used only for those in religious or professional communities (who can also be called sisters and brothers, but only, for example, the Plymouth Brethren).
A well-known search engine shows about 209,000 results for sistren, compared with about 29,200,000 for brethren. Wiktionary records “sistren (plural sistrens) (Rastafari) A close female friend, family member, or comrade”. Note that sistren here is singular, with its own plural sistrens, which is equivalent to saying childrens. A post on the Oxford’s blog doesn’t mention Rastafari but notes its use by feminists.
I suspect that Joss Whedon, the creator of the series and writer of this episode, used sistren because he thought that using sisters might sound as if she was referring to actual sisters, which might be possible given what we know about her at that point of the episode, but becomes less likely in hindsight when we learn more about her.
There’s a lot more to be said about the language used in this series. After all, another of Whedon’s creations is Buffy, the vampire slayer, which gave rise to the term Buffy Speak, or “a mode of language unto its own – one codified by a jumbling of nouniness and adjectiviage into languagey-bits that sound like your brain forgot words before spontaneously re-remembering them” (Kyle Kallgren), though Firefly doesn’t do it as much as Buffy apparently does (I haven’t watched any of the tv series, but saw the movie a long time ago and was decidedly underwhelmed, but then so was Whedon, whose original script was drastically altered in production).
By the way, Pages for Mac automatically changed sistren to sisters (but not brethren to brothers), and red-underlined it when I changed it back. WordPress’s editing window also red-underlines them. In fact, the subtitles have sister instead of sistren.