A  gender-neutral bathroom at the University of California at Irvine. (Lucy Nicholson/Reuters)

Despite its youth, “cisgender” has earned its place in the dictionary.

The word, apparently in use since at least 1994, describes a person whose gender identity corresponds to their sex at birth — such as a girl who continues to identify as female. It emerged in response to growing awareness of LGBT issues, as a way to describe what transgender is not.

“Most people can be described as cisgender,” according to Merriam-Webster, which included the word in a group of LGBT-friendly additions to its unabridged dictionary.

Others include “genderqueer” — an individual with a gender identity that does not cleanly qualify as male or female — and “Mx.,” a gender-neutral honorific.

“The new entries and senses offer a kind of snapshot of how exactly our language expands,” Associate Editor Emily Brewster wrote in a blog post announcing the introduction of more than 2,000 words to the Merriam-Webster unabridged dictionary. “It doesn’t happen quickly — we monitored many of these words for years before they’d met our criteria for entry — and it’s pushed by various fields and endeavors.”

The new additions include many words that have nothing to do with sex or gender, such as: “nomophobia,” the fear of being without access to a working cellphone; “FOMO,” a popular online acronym for fear of missing out; “hella,” slang for “a lot of”; and “dox,” the act of publicly identifying or publishing private information about someone, typically as a form of punishment.

Unlike those, however, the addition of words such as genderqueer lends legitimacy to terms long in use by the LGBT community.

“The move helps broadens public understanding of the increasing diversity of words that people within the LGBTQ community use to describe their identities,” the Human Rights Campaign said in a statement following Merriam-Webster’s announcement.

Cisgender first found legitimacy among lexicographers last summer, when the Oxford English Dictionary added an entry for the word, which OED traced to the late 1990s.

Merriam-Webster argues that cisgender is older than that: The oldest evidence of its use that editors there could find dates back to 1994. (Its first mention by this publication appears to have come much, much later, in a May 2013 blog post, according to searches of two databases.)

The prefix “cis” means “on this side,” and derives from the Latin “cis” or “citra,” according to the dictionary.

“Cis” is itself an adjective, in use since the late 19th century as an adjective describing that which is “characterized by having certain atoms or groups of atoms on the same side of the longitudinal axis of a double bond or of the plane of a ring in a molecule.”

Mx. is older still. A 1977 issue of the American magazine “Single Parent” contains the earliest use of the word uncovered by the dictionary.

And while it appears infrequently in print, the New York Times used it twice last summer, once in reference to someone who preferred it to Mr. or Ms. and once in an article about the honorific itself.

As with cisgender, Mx. is also in the Oxford English Dictionary.

https://twitter.com/MerriamWebster/status/723906850874339328

If it seems that dictionaries are adding words faster than ever before, that’s because in some cases, they are.

In a 2011 video, Merriam-Webster editor-at-large Peter Sokolowski explains — or “splains” — the historically slow, but sometimes accelerated way in which new entries are added.

“Whatever the speed, the process always begins with reading,” he said. “Merriam-Webster editors scan everything from newspapers, books and magazines to websites, menus and blogs, looking for words in their natural habitat for real evidence of the language in use.”

Once they spot a new word or new use of an old word, dictionary staff then document the citation.

“It’s by no means certain to get in, though,” Sokolowski said. “We need many such citations from varied sources and over a period of years in order to confirm that it’s a permanent addition to English. We don’t want to add a trendy word that might quickly drop from use.”

Linguists have long debated whether language should be defined descriptively (by how it is used) or prescriptively — according to a stricter, more centralized code.

Dictionaries tend to favor descriptivism, a defense of which The Post’s own Alexandra Petri offered up last summer when the Oxford English Dictionary added an entry for “twerk,” the provocative dance.

If a word has weaseled its way into our texts (of both the printed and 3 a.m. varieties) then it is no shame to record it. Words are roadmaps to thought. Dictionaries assemble those maps into an atlas. Here we are, it says. This is what is on our minds and on our tongues. It’s quite the record, from the frivolous (cake pop, hot mess) to the technical (crowdfund) to the powerful (cisgender).

Complain about such additions at your own risk. At the pace at which new entries are created, you’ll have hella reasons to be unhappy.