noun
cosecant
Mathematical term; used in trigonometry. Rare in everyday conversation.
余割は正弦の逆数です。
Cosecant is the reciprocal of sine.
正割 is secant (reciprocal of cosine), while 余割 is cosecant (reciprocal of sine).
From 余 (complementary) and 割 (division), referring to the complementary relationship with sine in trigonometry.