[Read more about dictionaries on Twitter and the perils of politicization.]

Merriam-Webster’s move, announced on Tuesday, reflects the fact that many nonbinary people use “they” as their singular third-person pronoun instead of “she” or “he.” (As an example of usage, the entry cites a June article in The New York Times.)

That the oldest dictionary publisher in the United States has added its imprimatur to this meaning of the pronoun could be seen as a powerful statement about evolving understandings of gender identity.

Or it could be seen as something much more elementary: a reflection of changing times.

The dictionary, after all, is more of a rearview mirror than a vanguard of change, said Peter Sokolowski, an editor and lexicographer with Merriam-Webster.

“If we see that a term is used frequently, then it’s going to get into the dictionary,” Mr. Sokolowski said. “We wouldn’t be doing our jobs if it weren’t reflecting the truth of the way language is used.”

Still, a major dictionary can add credibility to an existing term or definition, said Laura A. Jacobs, a therapist in New York who focuses on L.G.B.T .Q. clients and whose preferred pronouns include she, he and they — or none at all.