Cerulean.

You can almost hear Meryl Streep’s lips curling around the word, in character as her “The Devil Wears Prada” persona, fierce fashion mag editrix Miranda Priestly, these 10 years later.

The instant chick-flick classic debuted June 30, 2006, but it’s a rare person who can’t today recall at least part of the most fierce defense of the design houses that originate our trickle-down fashion finds.

In case you’re trying to tell the world that you take yourself too seriously to care about what you put on your back, that’s Streep’s monologue. She informs Anne Hathaway’s fashion assistant rookie character, Andy Sachs, wearing a blue sweater from a mall bargain rack and rolling her eyes at a very earnest decision-making process between two identical-looking belts before a magazine shoot, that “what you don’t know is that that sweater is not just blue, it’s not turquoise, it’s not lapis, it’s actually cerulean.”

What you don’t know is that the iconic scene almost didn’t make it into the movie at all, according to Aline Brosh McKenna, who wrote the screenplay for the movie (and also co-created current TV favorite “Crazy Ex-Girlfriend”).

There were always a few lines of Miranda dissing Andy’s fashion know-how in the script, but, according to McKenna, “it didn’t serve the narrative” in its original form. Then along came Streep.

“Meryl is really someone who is interested in explaining, having people understand always that Miranda had a serious job that she believed in and that she had faith in and she understood and a sense of importance of fashion in the world and why she thought fashion was important,” McKenna said. ”Meryl wanted to make it bigger.”

Instead of only being an attack on Andy, there was an opportunity for the lines to explain to the audience how seriously Priestly took her job and her duties as a fashion gatekeeper. Instead of an insult aimed at her assistant, the biting dialogue could be a look into how, as Priestly says, “that blue represents millions of dollars and countless jobs.” McKenna would expand the scene, infusing it with more meaning, send it to Streep and director David Frankel, and wait for feedback. Every time, the word came back: More.

“A few days before we were about to shoot it, maybe it was at a half a page, and it still stuck out as something that was cuttable,” says McKenna.

Again, Streep called for more. McKenna camped out at a Starbucks, where she had her aha moment: Miranda Priestly would never just call something “blue,” she’d know the precise shade of it.

She dashed off a list of blues to Streep and Frankel — lapis, azure, cerulean — and asked them to pick. “Meryl picked cerulean.”

In its final shooting form, the speech grew to slightly more than a page long, a rarity for a monologue in a mainstream movie.

“When I pressed Send, I was like it’d be cool if half of that ended up in the movie,” McKenna says. “Every word is in the movie.”

The speech had grown to a representation of how Priestly viewed her role in the world.

“Without that speech, you wouldn’t understand why it is so important to her,” McKenna says. “She is so aware that she is affecting billions of people, and what they pick off the floor and what they are putting on their bodies in the morning. That is her.”

And a page-long monologue is saying a lot (literally) for an actress like Streep, who has Oscars in triplicate gracing her mantle. When McKenna was writing the script before Streep was attached, she’d write provisional dialogue knowing that it might go out the window if the filmmakers got their dream lead, who’s so skilled at conveying things with a look or a gesture, where others need to spell out exactly what they mean.

The general guiding rule was, “If this is Meryl Streep, we don’t need a line here, but if it’s anyone else, we may need a line here.”

And if you’re wondering, yes, the withering stare that Streep deployed so often in “The Devil Wears Prada” was just as terrifying in person.

“The first day she was on set, I was there and it was the scene that Andy walks up to the desk and Meryl just turns around and looks at her, and that’s all she had to do, it was so scary,” McKenna laughs. “I threw my arm across Frankel’s chest like we were in a car wreck because it was so scary.”