Word

三平方の定理

さんへいほうのていり
Pythagorean theorem
Word

三碧

さんぺき
third of nine traditional astrological signs (corresponding to Jupiter and east)
Word

3K

三K
さんケー
difficult, dirty, and dangerous (work); three bedrooms and a kitchen (in real estate); three kilograms (or kilometers, etc.)
Word

三角柏

御津柏
みつのかしわ、みつのがしわ、みづのかしわ
leaves used for serving or offering sake, rice, etc.
Word

三損友

さんそんゆう
three kinds of bad friends (sycophantic, insincere, and glib)
Word

四三の星

しそうのほし
the Big Dipper; the Plough; the Plow
Word

三舎

さんしゃ
(in the ancient Chinese army) three days' march (approx. 36.5 km)
Word

三益友

さんえきゆう
three kinds of good friends (honest, sincere, and knowledgeable)
Word

三韓征伐

さんかんせいばつ
legendary military invasion of Korea in the 3rd century