Defining "plagiarism" is not simple, and its complexity is too seldom appreciated. This article offers a comprehensive plagiarism assessment rubric from a four-year study of analyzing students' plagiarism. From qualitative analyses of 120 students' paraphrase samples, we identified seven plagiarism dimensions and employed a five-point Likert-scale to rank each dimension's severity. Then, we enlisted editors, reviewers, and research supervisors to refine the severity of the plagiarism dimensions to articulate a plagiarism spectrum. We produced a Plagiarism Scoring Rubric to categorize 127 plagiarism combinations out of the seven plagiarism dimensions' composites. Finally, we described how the Plagiarism Scoring Rubric, accompanied by the severity indices, supports instructors in scoring students' plagiarism and enables students to understand proper crediting of prior work better when citing and paraphrasing.