Fathom vs. Phantom

A recent letter to the editor begins this way:

The most recent short-term fathom around the United States is the so-called outbreak of Ebola.

The writer wishes to point out that the reported Ebola threat to the United States was not only short-lived, but also insubstantial, a “short-term phantom.”

Here are the most common definitions of phantom as the word is used in modern English:

phantom [FAN-tm] (noun):
1. A thing (usually with human form) that appears to the sight or other sense but has no material substance; an apparition, a specter, a ghost.

2. Something merely imagined; an image in a dream, vision, etc. Also: a (usually delusory) notion or idea that plays on the mind or haunts the imagination.

phantom (adjective):
illusory, imaginary.

Examples of current usage:

Noun
Michael Crawford originated the role of the phantom in The Phantom of the Opera at Her Majesty’s Theatre in London in 1986.

I heard reports of the ice phantom, saw the secret spot where it was said to appear, [and] wondered about it for two years. 

Are Water Well Meters a Phantom or Reality?

Adjective
Approximately 5 to 10% of individuals with an amputation experience phantom sensations in their amputated limb, and the majority of the sensations are painful. 

Between King, Gohmert, and West, three separate House committees could decide to spend valuable congressional time combating a phantom threat. 

The word fathom is an extremely old English word. It is used with more than one meaning.

NOTE: The a in the first syllable of fathom is short, like the a in phantom, but the second syllable begins with the sound of th as in this. The two words do not sound alike.

As a term of measurement, a fathom is a length of about six feet, commonly used to measure the depth of water.

The original meaning of the noun fathom was “the two arms outstretched.” A fathom was the length represented by the arms of a full-grown man held straight out to either side.

The literal meaning of the verb, to fathom is “to encircle with the arms.” For example, a tree trunk might be too thick for a man to fathom (i.e., encircle with his arms).

When fathom came to be used to measure depth, the verb acquired a figurative meaning implying deep thinking and mental comprehension. For example:

The traditional philosopher hoped to fathom the world through the exercise of reason alone.

The catastrophe was an enactment of god’s moral justice, which mere mortals could not hope to fathom.

A far more common error than using fathom for phantom is the error of using phantom for fathom:

Examples of this error are especially plentiful in self-published works, both fiction and nonfiction:

I thought that’s what you said. I just can’t phantom it, that’s all. –The Chronicles of Chanute Crossing, Book Two: Nurtured in Purple.

I just can’t phantom in my mind the hardship they had to endure… –Slavery: Where Did it Come From?

I can’t phantom what the lead detective was thinking on this one. –Rainbows in the Dark.

The error is also common in contexts other than self-publishing. Here are examples from a variety of sources, including the testimony of a government policy director:

In a town with plenty of great sushi, I can’t phantom why anyone would want to go here anymore.

[A pet owner] just can’t phantom why anyone would want to steal a dog.

I can’t phantom why gas in Louisville exceeds the national average, time and time again.

We are just beginning to phantom the importance of broadband deployment.

I honestly can’t phantom why people don’t use spellcheck.

If what you mean is “I can’t understand,” it might be best to go with “I can’t understand.”