In the gif below, I'm making a fathom. To make a fathom is to stretch your arms out as far as they'll go.
(Source: original video)
If you already know that we measure length and distance in "feet," and that we measure the height of horses in "hands," then it won't surprise you to know that we used to measure width or depth in "fathoms."
Kind of like a 12-inch foot is about the length of a grown person's foot, a fathom is the width of a grown person's outstretched arms. A fathom is about six feet long.
(Source: original video)
When you fathom the depth of some water, you're measuring how deep it is in fathoms. Could you fathom the depth of the water in the image below? If the stick figure is about six feet tall, then I'm guessing this water is a little more than one fathom deep, but not quite two fathoms. (Source: original image)
Now, those are literal fathoms. When you talk about fish or mermaids (why not?) living fathoms below in the ocean, you're talking about how they live down deep in the water.
Here's the important bit! Because we figure out how deep something is by fathoming it—and because grabbing things with both your arms is kind of like grabbing ideas with your entire brain—the word "fathom" has come to mean "to figure out: to understand." In other words, if you fathom something, you get it: you know what it's all about. It's deep, yet you understand it.
Most of the time, we talk about how we CAN'T fathom something: we don't get it, we can't understand it, we're confused by it, and it's mysterious to us. Especially when it comes to people (because people are so complex) and when it comes to people's reasons for doing things.
When people and their actions seem so deep-down, so hidden, and so mysterious to you that you'll never understand them, say that you can't fathom them.
You can also say that things or people are fathomless, or unfathomable, meaning they are too deep, too hidden, too mysterious, or too confusing to ever be understood.
Make a flash card:
You can write your own definition and choose your own picture, or copy mine.
Term
Definition
Picture
fathom
to understand the "what," the "why," or the "how" of something
Write your own sentence!
You can use either of the two ideas I'll suggest, or you can invent your own. Include as much detail as you can!