This is the 8040th most frequent Russian word.
крепкой
"Крепкой" means "strong" or "firm" in English.
Here, "крепкой" describes the strength of the tea prepared, emphasizing its intensity or concentration.
Она заварила крепкой чаю для гостей.
She brewed strong tea for the guests.
In this sentence, "крепкой" refers to the strength and firmness of someone's handshake.
У него была крепкой хватка, когда он пожимал руку.
He had a firm grip when he shook hands.
Here, "крепкой" modifies "basis" to signify reliability and sturdiness.