chiefsubject
nounUK /tʃiːf ˈsʌbdʒɪkt/
US /tʃif ˈsʌbdʒɛkt/
The main thing that a story, talk, or lesson is about.
The chief subject of today's class was how plants grow.
OTHER MEANINGS
2. The most important person or thing being discussed or studied.
The chief subject of the meeting was the new playground.
3. The leading topic in a book or report.
Her report's chief subject was recycling at school.
4. The main area someone studies or works on.
Math is his chief subject at school.