Definition of reckonmaster in English:
reckonmaster
noun ˈrɛk(ə)nˌmɑːstəˈrɛk(ə)nˌmastə
rare, historical A mathematician; an arithmetician; an accountant.
Origin
Late 16th century; earliest use found in John Dee (1527–1609), mathematician, astrologer, and antiquary. From reckon + master.