Quick answer
To defuse is to remove the danger from something — literally removing a fuse from a bomb, figuratively calming a situation. To diffuse is to spread something out over an area. "Diffuse the tension" is the frequent error; you defuse tension, you diffuse light.
The core difference
One removes danger; the other spreads something around.
- defuse — make safe, calm: defuse a bomb, defuse the row.
- diffuse — spread out: diffused light. Also an adjective: a diffuse argument (unfocused).
The fuse is the clue
Defuse contains fuse, and that is exactly the image: taking the fuse out. If nothing is being made safer, the word is wrong. Diffuse is from Latin diffundere, to pour out in all directions.
The adjective
Diffuse also describes writing that is spread thin and unfocused — a diffuse and rambling report. That is a criticism, and it has no counterpart in defuse, which has no adjective form at all.
Frequently asked questions
Is it "defuse the situation" or "diffuse"?
Defuse — the image is removing a fuse to make something safe.
What does diffuse mean as an adjective?
Spread thin and unfocused, as in a diffuse argument — usually a criticism.
How do I remember which is which?
Defuse contains fuse. If nothing is being made safer, you want diffuse.
