I’m currently reading a medieval text on mining and I finally got around to looking up what a “fathom” is, as in the unit of measure. Today it only survives as a nautical measure, but originally it was used as a general unit of length, and corresponds to the length of someone’s outstretched arms, measuring from one fingertip across the breadth of the chest to the far fingertip. Think the average human height, since human height roughly equals wingspan (hence the famous Vitruvian Man depiction), but for practical reasons it’s usually easier to measure something fingertip-to-fingertip than trying to line up your height just so, hence the definition of fathom in terms of wingspan.
I’m struck by how similar this ancient measure is to how kids today describe the size of something. “It’s THIS big” (arms outstretched). It really is a natural measurement
Quick detour: if you want to sound erudite and make a bold claim that your ignorance is shared by all, you can call something “unfathomable.”
See the root word there? Unfathomable describes something that is not “fathomable.” And “fathomable” comes from—you guessed it—“fathom.”
So when you’re making the erudite claim that some concept is “unfathomable,” what you’re really saying is that it’s THIS hard (outstretched arms) to understand,
The dictionary doesn’t go into detail about the original metaphorical usage, but I’m guessing it’s more based on the action of depth sounding (using a sounding line measured in fathoms), however I prefer my interpretation for reasons of humor.
but even bigger than that.
Really kids are just more erudite than you think.