核 is one of the most commonly used Japanese kanji, and it also has a lot of special readings in addition to the standard onyomi and kunyomi readings.
ONYOMI 音読み
KUNYOMI 訓読み
カク kaku
Examples
この核時代にあっては、世界中どこの国だって安全ではない。No country under the sun is safe in this nuclear age.今日若者たちは、自分には何の罪もないのに、国際的な悪感情と核破壊の脅威によって分裂した世界に生きている。Today young people find themselves, through no fault of their own, living in a world torn by international bitterness and the threat of nuclear destruction.