sinful, a sinner: a person whose life falls short of God's standard, or the quality of being marked by sin
At its core this word labels someone as a sinner, a person who lives outside what God requires. The same word does three jobs in the New Testament that are worth keeping apart.
First, it names the basic moral standing of a person before God: guilty, in the wrong, needing forgiveness. Paul uses it this way when he says Christ died for us while we were still sinners, and it is how the tax collector in the temple describes himself.
Second, the Gospels use it almost as a social label. "Tax collectors and sinners" was a stock phrase for a recognized class of people whom the religiously strict treated as beyond the bounds of the law. Often the word is in the mouth of others, drawing a line between the respectable and the outsiders, and Jesus pointedly crosses that line.
Third, it works as a plain adjective meaning sinful, describing a thing rather than naming a person, as in "this sinful generation" or sin shown to be sinful beyond measure. All three uses share one idea: being characterized by sin.