Quick answer: Dead means no longer alive — it describes a state: The plant is dead. Deadly means able to cause death — it describes a quality or potential: This snake’s venom is deadly. For a fuller definition, see the Cambridge Dictionary entry for ‘dead’.
Comparison Table
| Word | Part of Speech | Meaning | Example |
|---|---|---|---|
| dead | adjective / adverb | no longer alive; completely (informal adverb) | The battery is dead. / She was dead right. |
| deadly | adjective / adverb | likely to cause death; extremely (informal) | A deadly disease. / It was deadly boring. |
Using Dead
Dead is an adjective describing something that has already lost life or stopped functioning. It is a factual, completed state with no degree — something is either dead or it is not.
The flowers in the vase are dead.
They found a dead bird on the pavement.
My phone battery is dead.
Latin is often called a dead language.
Dead as an Informal Adverb
In informal British English, dead can function as an intensifying adverb meaning “completely” or “absolutely”: dead tired, dead right, dead easy, dead slow.
You’re dead right about that.
It was dead easy.
Using Deadly
Deadly is an adjective meaning “capable of causing death” or “very dangerous”. Unlike dead, it refers to potential — something that has not necessarily killed yet but could do so.
The spider carries a deadly poison.
Driving without a seatbelt can be deadly.
She aimed at the target with deadly accuracy.
The film was deadly dull. (informal: extremely)
Deadly Sins and Fixed Phrases
The phrase deadly sins (the seven deadly sins) is a fixed religious and cultural expression. Deadly here means “spiritually fatal” rather than physically lethal.
Pride is considered one of the seven deadly sins.
The detective laid a deadly trap for the suspect.
Common Mistakes
✗ The deadly fish was lying on the shore. (ambiguous — implies the fish can still kill)
✓ The dead fish was lying on the shore.
Note: if the fish has died, use dead; if the fish’s venom can kill, use deadly.
✗ This disease is dead. (wrong — implies the disease itself has died)
✓ This disease is deadly.
✗ It was deadly right. / It was dead boring. (mixing registers)
✓ It was dead right. / It was deadly boring.
Note: both are British informal intensifiers, but they pair with different adjectives by convention.
Quick Check: Dead or Deadly?
Four questions — choose the correct word for each sentence.
1. “The cobra’s bite is ___.”
2. “We found a ___ mouse in the garden.”
3. “Smoking is a ___ habit.”
4. “The old tree in the park is ___.”
Frequently Asked Questions
What is the difference between dead and deadly?
Dead describes something that has already lost life or stopped functioning. Deadly describes something that is capable of causing death. A dead snake cannot harm you; a deadly snake can.
Can dead be used as an adverb?
Yes, in informal British English. Dead functions as an intensifier meaning “completely” or “absolutely”: dead tired, dead right, dead easy, dead slow.
Can deadly mean “extremely”?
Yes, in informal usage. Deadly can intensify adjectives: “deadly boring” or “deadly serious.” This is common in Irish and some British English.
Is “a deadly person” the same as “a dead person”?
No. A dead person is someone who has died. A deadly person is someone who is dangerous or likely to kill. These are very different meanings.
What are the seven deadly sins?
The seven deadly sins are pride, greed, wrath, envy, gluttony, sloth, and lust. Here, deadly means “spiritually fatal” in a religious context, not physically lethal.
Can I say “dead silence”?
Yes. Dead silence is a fixed idiom meaning complete, absolute silence. Here, dead acts as an intensifying adverb. Deadly silence is also used but less common in British English.
What is the noun form of deadly?
Deadly does not have a common noun form. The related noun is deadliness. Dead has the noun death. The verb is die (past: died).
Is “deadly accurate” correct?
Yes. Deadly accurate means extremely precise, often to a lethal degree. It is used to describe shooters, weapons, or even arguments that are powerfully effective.
How do I use dead and deadly in IELTS or TOEFL?
Use dead in formal writing to describe a factual state (dead cells, a dead language). Use deadly to describe potential lethality (a deadly virus, deadly consequences). Avoid the informal adverb senses in formal writing.
Are there other -ly adjectives like deadly that look like adverbs?
Yes. Words like friendly, lively, lovely, lonely, and likely end in -ly but are adjectives, not adverbs. Deadly follows this same pattern — it is primarily an adjective despite the -ly ending.