The will stated that the house would return to him as a reversionary right when his grandson came of age.

reversionary 是由名词 reversion（复归、归还）加上形容词后缀 -ary 构成的形容词。reversion 来自动词 revert（返回、恢复原状），表示"回归到原所有者"的法律概念。 reversionary right 指"复归权"，即财产在特定条件满足后（如孙子成年）自动回归原所有者的法定权利。