Easy; simple; not difficult (adjectival noun indicating something is easy or straightforward).
彼にとってこの問題は容易だ。
This problem is easy for him.
設定は容易だが、効果を確かめる必要がある。
The setup is simple, but it's necessary to check the effectiveness.
成功は容易ではないが、諦めないで努力しよう。
Success is not easy, but let's keep trying and don't give up.