An example of chiasmus is the line “By day the frolic, and the dance by night” from The Vanity of Human Wishes, a Juvenalian satire by Samuel Johnson.
The first part of the sentence (“by day the frolic”) begins with a time of day and is followed by an event. In contrast, the second part of the sentence (“and the dance by night”) starts with an event and concludes with a time of day. Therefore, the second half serves as a conceptual mirror image of the first. While the exact words are not repeated, the underlying concepts are reflected.