low-key

Low-key would appear to have musical origins, characterizing something has having a deeper, more muted, or darker tonal register. We can find low-key for “of a low pitch” in the early 19th century. Charles Dickens, for instance, wrote of it that way in his 1844 novel Martin Chuzzlewit:

She continued to sidle at Mr. Chuffey with looks of sharp hostility, and to defy him with many other ironical remarks, uttered in that low key which commonly denotes suppressed indignation.

In 1857, the reading primer Introductory Lessons in Reading and Elocution used low-key for the tone of voice that a person uses when speaking softly or whispering. We can see, then, how low-key would, by the 1890s, refer metaphorically to something quiet, restrained, or modest. A century later, low-key expanded for something more casual or easygoing—chill.

By the late 2000s, low-key made a perhaps not-so low-key jump: It became an adverb characterizing doing something with a low intensity, moderation, or subtlety.

Low key wishing I was still on vacation. I got more done that way lol

— KeishaNicole (@KeishaNicole) August 3, 2009

Taco tuesdays was low key poppin… i enjoyed myself….. seen some ppl i haven't seen in a while my bbm pin is 244760a9,,,,, add me

— Nick Nailor (@KingSaul21) August 5, 2009

@WilliePA low key she spits like Wayne…

— AlFredo Santana (@PerfGawd) May 5, 2009

By 2010, an Urban Dictionary noted the adverbial low-key, which appears to have been further popularized by hip-hop music in the mid-2010s. Chance the Rapper’s 2012 “U Got Me F****d Up,” for example, contains the lines: “Coolin’ with Mikey, low-key I rock / Mags on my bike, Tay like he chuck.”