one day, 24 hours / the daytime, the period from dawn until dusk / (figuratively) a short period of time / one day, someday, an unspecified day / the first day of the month

(linear algebra) positive-definite matrix

(linear algebra) positive-semidefinite matrix

(literally) one side / everywhere, all around, the whole area / one viewpoint, one opinion or way of thinking / the front page of a newspaper

(idiomatic, proverb) be quick on the uptake, understand the whole situation from just a few clues

千載一遇: once in a lifetime

once in a lifetime

people working together with one mind

Uniform Resource Locator

first discoverer (used especially in reference to the discovery of a dead body)