A knack; a trick or tip — the essential point or know-how needed to do something well.
料理の骨は最初に包丁をよく研ぐことだ。
The knack for cooking is to sharpen your knife well at the start.
英語を話すコツ（骨）は、毎日少しずつ声に出すことだ。
The key to speaking English is to practice speaking out loud a little every day.
工具の使い方には骨があるから、先輩に教えてもらおう。
There are tricks to using these tools, so let's have a senior show you.
A bone; a member of the skeleton — the hard tissue that supports the body.
転んで骨を折ってしまったので、入院した。
I fell and broke a bone, so I was hospitalized.
人間の頭蓋骨（ずがいこつ）は脳を守る役割がある。
The human skull protects the brain.
魚を食べるときは小骨に注意して食べてください。
Be careful of small bones when eating fish.
Cremated remains (bones left after cremation); ashes/bony fragments often kept in an urn.
お寺に遺骨を納めるため、骨を骨壺に移した。
To inter the remains at the temple, we put the bones into an urn.
戦没者の骨は慰霊碑の近くに埋葬された。
The remains of the war dead were buried near the memorial.