Answer
The full name is tin(II) oxide
Work Step by Step
The charge on Sn must be 2+ for the compound to be charge-neutral with the $O^{2-}$ anion. The name for SnO is the name of the cation, tin, followed by the charge of the cation in parentheses (II) and the base name of the anion, ox, with the ending - ide. The full name is tin(II) oxide.