Origins
To be robust is to be like an oak. The word comes from Latin rōbustus, meaning 'hard' or 'strong', from rōbur — the Latin name for the common oak (Quercus robur, still its scientific name). Rōbur also meant 'hard timber' and, by extension, 'strength' itself.
The Romans measured strength against wood. Oak was the hardest timber available in quantity, and rōbur became shorthand for solidity and endurance. Roman builders prized oak for structural beams, ship hulls, and fortifications. A robust thing was built with the reliability of oak.
The connection between the tree and the concept may trace even deeper. Some etymologists link rōbur to Proto-Indo-European *h₁rewdʰ-, meaning 'red', referring to the distinctive reddish heartwood that makes oak so hard and durable.
Latin Roots
Corroborate descends from the same root. Latin corroborāre meant 'to strengthen together' — as oak beams strengthen a building when assembled. To corroborate a story is to add supporting timber to its structure.
In modern English, robust has moved from the forest to the server room. A robust system, a robust economy, a robust debate — each borrows the oak's reputation. The word appears constantly in software engineering, where a robust application is one that does not break under pressure. The oak has become a metaphor for reliability itself.