triangular prism

three years; the third year / (education) the third school year / (figuratively) a long period of time, several years

three years; triennial / three years old

three years of age, three years old

You should treasure every encounter, for it will never recur.

vicissitudes, the way that the world or a person prospers one day and declines the next

dotting the i's and crossing the t's

successive series of questions and responses

a lucky day, auspicious day

(rare) one's birthday