Lack is a verb and noun in English, meaning the state of not having something or not having enough of something.
Common usages of lack include:
1. As a verb: "She lacks confidence in public speaking."
2. As a noun: "There is a lack of fresh water in this area."
3. In phrases: "for lack of", "no lack of", "lack thereof"
Synonyms: shortage, deficiency, absence, scarcity