Used to express a sufficient condition, often paired with 就 jiù, 都 dōu, or 便 biàn in the following clause to mean "if only" or "provided that"

time and effort spent on a task; labor

deep; far from the surface or outside (physically or figuratively); having a large distance from top to bottom

Meaning "to grind an iron pestle into a needle"; an idiom used to describe how anything can be accomplished if one works hard and stays persistent. It refers to a story where the famous poet 李白 lǐ​bái was inspired to continue his studies after seeing an old woman trying to grind a thick iron bar into a sewing needle.