Noun:

अनिष्‍टमयता, हानिप्रदता,

harmfulness's Usage Examples:

Temperance in the use of alcohol has followed the demonstration not only of its unimportance as a food or tonic, but also of its harmfulness, save in very small quantities.

Prevention education programs are also widely used to inform young people of the harmfulness of substance abuse.

When it comes to the harmfulness of video games, the realistic violence that is portrayed rates at the top of most lists.

Synonyms:

injuriousness, virulence, destructiveness, insidiousness, virulency,

Antonyms:

nutritiousness, nutritiveness, quality, healthfulness, wholesomeness,