A sermonar is similar to a seminar in that there is a topic and one or two presenters. Seminar is usually more like a workshop, which can be as short as several hours, or even as long as several days, with Q&A periods. A sermonar is no longer than 2 hours, and is given during the morning worship period at a church.
My husband and I recently gave a sermonar on Christian dating and marriage at a church in Santa Monica, California during the 11:00 a.m. worship period. It was well-received, and we went away with lots of helpful feedback. (True story!)