noun
Used in school contexts to refer to the first class of the day.
一限目は数学の授業です。
The first period is math class.
一限目に遅刻してしまった。
I was late for the first period.
Compound of 一 (いち, 'one') + 限目 (げんめ, 'period'). 限目 is a suffix used to count class periods.