What part of speech is unthoughtfulness?

Unthoughtfulness can be categorized as a noun.

Parts of speech

• 1. unthoughtfulness is a noun, singular of unthoughtfulnesses.

Inflections

Noun

• Singular

  Plural
• unthoughtfulness 

  unthoughtfulnesses 

• Singular: unthoughtfulness 
• Plural: unthoughtfulnesses 

What does unthoughtfulness mean?