Why is there a "b" in subtle?

If you know this word by sight, you might not know how to say it. And if you know it in conversation you might not know how to spell it.

For those of you in the first camp, we'll give you a hint: that "b" is subtle. So subtle, in fact, as to not be heard at all. It's a silent "b," like the "b" in thumb and debt. The word actually rhymes with shuttle.

And for those in the second camp: this is the word that sounds like it should be spelled "suttle."

So what is that pesky "b" doing there anyway? Is that sub at the beginning of the word related to the sub in submarine and subterranean?

Yes, it is. Subtle comes ultimately from a Latin pair: the prefix sub-, meaning "under," and tela, meaning "web." The two were joined in Latin subtilis, meaning "finely woven." The word was literal; it was originally a weaving term. But over time subtilis developed figurative uses, and was applied in many cases in which the word fine would work as well: to describe details, distinctions, and tastes, among other things.

When subtle came to first be used in Middle English its meaning was very much in this same lineage. It meant "perceptive, refined," and was used to describe people known for their clear thinking—such as philosophers—and things, such as analysis or reasoning, that demonstrated such thinking.

One more thing about the spelling of subtle: like many words that have been in the language for centuries, this one took numerous forms before settling into its current spelling. Many of the forms didn't include the "b" at all—and it's believed that the "b" was probably never pronounced in English. The "b" spellings that were used were a nod to the Latin subtilis. And much to the chagrin of those in favor of phonetic spellings today, one of them came out on top.