Clipping of 第三インターナショナル (“Third International”).

(history, communism) Synonym of コミンテルン (Komiterun, “Comintern”); the Third International

the thirtieth day of a month / thirty days

the final day of a month / the thirtieth day of a lunar month

thirteenth day of the month

(mathematics) equilateral triangle

(idiomatic) thoughts buried deep inside the heart

(idiomatic) one's mind; one's inner feelings; (a decision hinging on) how someone feels about it

e-mail with only the most basic elements

(education) meeting held between a homeroom teacher, student, and guardian