I would say that "low-key" is a strange phrase to use, as it's essentially jazz slang (like a low, bass note), while also somewhat outdated. "Low-key" would be how you would ask for drugs at a party or a show. You want to buy drugs, but you don't necessarily want everyone to know you want to buy drugs, so you ask the right person who knows the guy that knows the guy - perhaps you whispered your request all, "low-key" like.

I would sort of agree that it's a strange place to put it in this sentence. It kinda needs an em-dash or something:

"Walton knew: the bicycle is -- low-key -- one of humankind’s greatest inventions"

But I would edit that all out as it's not needed and disturbs the flow of the sentence.

I think what the author is trying to say is more, "underappreciated".

Walton knew: the bicycle is one of humankind’s most underappreciated, yet greatest inventions.

Perhaps in the vein of indoor plumbing, tho many people go without riding bikes, while none of us who have indoor plumbing would give it up.

Or maybe even "under the radar". You know the best place to eat in town, but it's just some hole in the wall managed by a single guy, but god-damn do those mashed potatoes slap.

Bicycle love isn't something advertised, like a car is. You get on a bike and you fall in love with it. Attraction over promotion.

In this context, it just means "underappreciated" or "less widely known or acknowledged than other inventions of similar magnitude of impact".

I don't think it's millennial slang; I'm almost 50 and I've heard it used this way all my life.

However, I was vaguely aware that it had some original, more technical meaning, specific to some discipline like composing music or something like that. My interest in investigating was limited, though, so I only asked GPT-4o, who claimed:

> Originally, the term "low-key" was used in reference to a lighting technique in photography and cinematography. It described a style that utilized less lighting to create a mood of intimacy, mystery, or dramatic contrast. This usage emphasized the subtle, understated nature of the lighting, which is less intense and less prominent than high-key lighting. Over time, "low-key" evolved to take on broader meanings, including understated, subdued, or not seeking attention, before arriving at its contemporary connotation of something or someone being low-profile or modest.

(I'll accept that, I guess, unless disputed/refuted here by the actually sentient.)

That an interesting question! I had never seen that usage of “low-key” either.

Some similar examples found on the web:

“Astro Bot is low key one of the best Sony franchises and I’ll fight anyone who says otherwise.”

“Nitro navy is low key one of our fave colours on the Kreissage RS. What’s yours?”

“I think Flora is low key absolutely hysterical.”

“Am i the only one who thinks this soundtrack is lowkey really good?”

“Feels good, it's my first time buying a [chest] binder.... i saw reviews saying like oh i should've bought a smaller one but nope it is lowkey too small but i sure can squeeze myself into it and it looks great.”

See also:

https://www.merriam-webster.com/wordplay/words-were-watching...

https://grammarist.com/idiom/low-key-and-lowkey/

https://www.reddit.com/r/AskABrit/comments/11uizro/please_so...

It's a phrase my kids (aged 17-25) use a lot. It just means it's not a shouty, in your face thing, but happening on the quiet.

I see it used as a conversational gambit to downplay the impact of something you’re about to say (which might otherwise be received as over-the-top, or sensationalised, or aggressive, or ripe for someone to argue with).

It’s a bit similar to how one might start a statement with “Honestly…” - to flag that what’s coming might be more than usually challenging or blunt.

Something that's not drawing much attention.

I think it means something like "secretly". It's millenial slang.