This is the 5266th most frequent Japanese word.
鰹
Bonito (a type of fish).
鰹 is used as a general noun referring to the fish itself.
鰹は魚の一種です。
Katsuo is a type of fish.
鰹 is referred to in the form of katsuobushi, dried and smoked bonito flakes, as an ingredient.
この料理には、鰹節が使われています。
This dish uses katsuobushi.
鰹 is mentioned in the context of fishing, referring to the activity of catching bonito fish.