Effortless
Smooth
な adjective
Something that is round and slippery just moves around with no trouble at all. It is so effortless in how it slides around. It is also super smooth.
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
英語で円滑なコミュニケーションを取るために、最も重要なことは何だと思いますか？
What do you think the most important things are to have a smooth conversation in English?