'The last Will and Testament of Thomas Blise ... made the seventh Day of the eighth month; 1647 the said will allso Exhibbited unto the Court holden at new Plymouth the eighth of June 1649, ... unto Nathaneell the son of my sonninlaw Nicolas Ide ...'
It was common in the 1600s to use the term son-in-law for step-son. It is believed that this was the case in this will.