intercalary; extra, surplus
Depicts a king (王) in a doorway (門), as part of a ceremony marking the beginning of the extra month sometimes inserted into the lunar calendar.
《說文》：“閏，餘分之月，五歲再閏。告朔之禮，天子居宗廟，閏月居門中。从王在門中。《周禮》曰：‘閏月王居門中，終月也。’”