"Lark about" is a colloquial expression that means to act in a playful, light-hearted way or to behave in a mischievous manner. There are various synonyms for "lark about" that convey a similar sense of fun and playfulness. Some of these terms include "cut up," "frolic," "joke around," "monkey around," "muck around," "play around," "mess around," "goof off," "act silly," "have a laugh," "make mischief," and "pull pranks." All of these phrases can be used to describe engaging in frivolous or amusing behavior, often with a group of friends or people you feel comfortable around. Whether you're larking about, goofing off or cutting up, it's all about having a good time!