defuse vs. diffuse  

What is the difference between defuse and diffuse?

The words defuse and diffuse are very often confused due to their similar pronunciations as well as a perceived overlap in meaning.
When pronounced carefully, the “de-” in defuse (/diˈfjuz/) receives a bit of extra stress, and the E takes the “long” pronunciation (/i/) found in words like theme or discrete. On the other hand, the I in diffuse (/dɪˈfjuz/) takes the standard “short I” sound found in words like rip or dip. In casual, everyday speech, though, the stress on the first syllable of both words is often reduced, resulting in the same pronunciation: /dəˈfjuz/.
The verb defuse is formed by combining the prefix “de-” (in this case, meaning “undo”) with the noun fuse (a trigger used to detonate an explosive device) to mean “to remove, disable, or destroy a fuse from an explosive device,” as in:
  • “Officers were able to defuse the device before it was able to explode.”
By extension, defuse can also be used figuratively to mean “to subdue, lessen, or remove tension, hostility, or danger.” For instance:
  • “The secretary of state has been in intense negotiations with the foreign ambassador in an attempt to defuse the crisis in the region.”
  • “He tried telling a joke to defuse argument, but it didn’t go over very well.”
Diffuse, on the other hand, is derived from the Latin diffusus. It is also primarily a verb, most often meaning “to spread, scatter, or pour out widely,” as in:
  • “The smoke from the burning paper diffused slowly throughout the room.”
  • “Rumors surrounding his source of income have diffused across the Internet.”
By extension, diffuse can also mean “to weaken or make less intense due to scattering,” as in:
  • “The dirty window panes diffused the sunlight into a murky haze.”
(Note that diffuse can also function as an adjective, usually meaning “widely spread, scattered, or dispersed,” as in:
  • “The room was filled with a soft, diffuse light.”
  • “The government’s efforts have been too diffuse to be of any real effect.”
In this usage, diffuse is pronounced with an /-s/ sound at the end, rather than /-z/: /dɪˈfjus/.)
It is the figurative application of diffuse that causes most confusion for writers, as it seems logical to use it in a way similar to the figurative use of defuse. For example, “diffusing tension” might seem correct, as it could be interpreted as meaning “making the tension less intense.” Because this is so widespread, some sources even consider this as being correct.
However, most grammar and spelling resources do not accept this, arguing that the only reason diffuse can mean “to weaken” is that the thing being weakened is spread thinly across a wider area, which is not what happens when one lessens or weakens tension, danger, etc. When referring to making situations less tense, hostile, or dangerous, use defuse because it will always be correct.

Spelling Tricks and Tips

When trying to determine which spelling to use, remember that “de-” means “remove,” and you’ll know that defuse is the right word to remove a fuse from an explosive—or an explosive situation. Diffuse has a different use altogether.

1. Choose the sentence in which defuse is the correct spelling.

2. Choose the sentence in which diffuse is the correct spelling.

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