Harmful definitions
Causing or capable of causing harm; injurious.
adjective
The definition of harmful is something that causes damage or is able to be hurtful.
A chemical that causes you to become sick is an example of a chemical that would be described as harmful.
adjective
Causing or able to cause harm; hurtful.
adjective
Of a kind likely to be damaging; injurious.
Wear a hat to protect your skin from harmful sunlight.
adjective
Origin of harmful
From harm + -ful.