Diffuse and defuse are easily confused words.
The spell-check application of most word processing software programs would not catch a slip-up of these two words. Spell-check is looking for words that aren’t in its dictionary, and words that resemble words in its dictionary, but are possibly spelled wrong. Spell-check isn’t perfect. It doesn’t know and can’t guess what word you wanted, or what word you meant, it can only judge the words on the page. If you used words that are all spelled correctly, it gives you a pass anyway.
Autocorrect suggests words that start with the same letters. It’s suggesting what word you may want to save time, but quite often, its suggestions are pretty off base. They don’t help you out, but they do make you laugh.
Diffuse (pronounced “dih-fewz”) is a verb. It means to pour, spread, or scatter a substance.
In physics, it means to spread via diffusion. This means molecules or ions intermingling as a result of thermal stimulation.
Defuse (pronounced “dee-fews”; UK: spelled defuze) is a verb. It means to disconnect an object from its energy source, like a bomb or explosive. Figuratively, it can mean to tone down a situation or scenario from dangerous or threatening circumstances.
The following story uses both words correctly:
Deja had an instinctive gift with electrical wiring, she defused bombs for the US Army. After twenty years of service, she retired and pursued agriculture and botany. She was eager to save the environment. She would hand out tree saplings, and diffuse seeds in abandoned fields. She would and share environmental awareness information with anyone willing to listen.