Definition of Lighten up:
A colloquial term used casually to tell another person to be less tense or to calm down. Because the term is casual in nature, it might be used between two individuals who have a close relationship with one another. It can be said between two employees on the same level, or from a supervisor to his or her subordinate.
The act of making something less heavy or lighter; for example, removing inventory from a truck.
The act of liquidating positions held in an investment portfolio by selling holdings in exchange for cash. For example, selling a portion of stocks or bonds will lighten up an investment portfolio.
Meaning of Lighten up & Lighten up Definition