The plain meaning of the word "deadly" is something that can cause or has caused death. It refers to a weapon, situation, disease, or other entity with the ability to end life or take it away.
Usage examples
The snake's venom is deadly, causing paralysis and eventual death.
He was involved in a deadly car accident, resulting in multiple fatalities.
The assassin's accuracy with a sniper rifle is deadly, making him a formidable threat.
The deadly virus spread rapidly, leading to a global pandemic.
The chef warned the customers about the deadly shellfish, as consuming it could be fatal.
The mountain climber lost his grip and fell, narrowly escaping a deadly drop.
The drug overdose proved to be deadly, claiming the life of the young individual.
The deadly combination of alcohol and driving is responsible for numerous accidents.
The serial killer's modus operandi was particularly deadly, leaving no trace of evidence.
The consequences of flea infestation will be terribly uncomfortable for most affected cats and can be the source of deadly disease for some. (www2.vet.cornell.edu)
Recent new stories and rumors about vaccines have led to outbreaks of deadly diseases once assumed to be eliminated. (freewayinsurancetx.com)
As with deadly shootings in the past, some of the focus has been on the companies that make the weapons and ammunition and the people and companies that own them. (cnbc.com)