A certain form of the japanese Kwanei Sen (q.v.) with waves or curved lines on the back. They are sometimes called Shi Mon Sen or four Mon Sen, being valued at four of the regular pieces. Various other coins with waves on them were called Nami Sen, such as one of the coins of Akita Province.
Synonyms: Wave Sen
Source: Frey's Dictionary (American Journal of Numismatics, Vol. 50, 1916)