grandchild
n. countable A2 Elementary US //ˈɡɹænˌtʃaɪɫd// UK //ɡɹˈændtʃaɪld// grand·child
n. the child of your son or daughter.
n. the offspring of one's child, regardless of gender.
She loves spending time with her young grandchild.
The elderly couple traveled across the country to attend their first grandchild's graduation ceremony.
The distribution of the family estate was carefully structured to ensure that each grandchild would receive an equal share upon reaching the age of majority.
From grand- + child.
Usage
The plural form is 'grandchildren'.