means Enduring pain, hardship, or emotion without complaint or visible reaction, keeping a calm and uncomplaining front.

from From the Greek Stoikos, named for the Stoa Poikile — the "Painted Porch" in Athens where the philosopher Zeno taught his followers around the 3rd century BCE. The school took its name from the porch itself, so a "stoic" is literally a person of the porch: someone schooled in accepting fate calmly. Over centuries the capital-S philosophy shrank into the small-s adjective we use for anyone who takes a punch without flinching.