This is the 109th most frequent Dutch word.
groot
Large.
In this sentence, 'groot' is used as an adjective to describe the size of the cat.
De kat is groot.
The cat is big.
In this sentence, 'groot' is used as an adjective emphasizing the magnitude of 'belang' (importance).
Dat is een groot belang.
That is of great importance.
Here, 'groot' is part of the compound noun 'grootouder', meaning grandparent, referring to one of someone's grandparents.