to breathe one's last: to die as the final breath goes out.
This is a solemn, elevated word for dying. It pictures the moment life ends as the last breath leaving the body, and it is a step up in dignity and weight from the plain, everyday verb for dying. The two words are often used one after the other, as in "he breathed his last and died," where this word supplies the image of expiring and the ordinary word states the bare fact.
It describes very different deaths. It closes the accounts of the great fathers of Israel: Abraham, Isaac, and Jacob "breathed their last" full of years and were gathered to their people, so readers sometimes hear in it a good and peaceful end. But the same word is used for death under judgment: every living thing that expired in the flood, and the people who cried in the wilderness that they would all perish. The word itself does not decide whether a death is gentle or terrible; that comes from the setting.
In Job and the Psalms it becomes the language of lament and reflection. Job repeatedly wishes he had expired at birth, or says he is ready to breathe his last, and the psalmist watches all creatures give up their breath and return to the dust the moment God takes their breath away. Across all these settings the core picture holds steady: the final breath goes out, and life is over.