Essential
Noun and な adjective
ふかけつ
ビーチに行く時は、日焼け止めが不可欠です。
When I go to the beach, sunscreen is essential.
日本語がペラペラになるのに不可欠なことは何だと思いますか？
What do you think would be essential to becoming fluent in Japanese?
美味しいベーコンは、サクサク仕事を進めるのに不可欠です。
Tasty bacon is indispensable in promoting efficient work.
It's not possible to lack. It is indispensable and essential, so don't lack it!
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.