The primary cause of my diarrhea is probably the soft serve I ate just now.
The main cause behind the near-miss is that the train sped up when it wasn't supposed to.
The main causes behind many conditions like cancer and autism are still unknown.
The main cause is the main cause or the primary cause.
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.