[timb07]

"Trimester" is a word commonly used in English in relation to the stages of pregnancy.

[repsilat]

Mm, and it's good to know it's etymologically closer to "three months" than "third-length period".

(TIL also that "semester" means "six months". I'm an idiot, I thought it was "half-length period". Like "semi" I guess.)

[matthberg]

Also in the academic world where there is a quarter year system used (3 trimesters and summer break).

[wnoise]

Also some college use it rather than quarter or semester systems.