robust

A learned borrowing from Latin rōbustus, and in comparison it mostly keeps the longer forms. More robust and most robust are the usual forms, while robuster and robustest exist but are uncommon. In this broad sense it sits close to sturdy. Its natural opposite is fragile, the word for what the same adverse conditions would break.

Here the strength is in the body, though it reaches past people to things built to last, as in a robust wall. Robust health is the fixed pairing to know. Size often comes with the strength. Trollope, in Phineas Finn (1869), sets more robust beside stronger and larger, and adds physically to pin the word to the body rather than the character.

Systems engineering asks what happens after something breaks. A robust system loses parts without losing the whole: a network routes around failed nodes, and an ecosystem survives the loss of some species. The test is partial damage. That separates it from the software sense, where the danger is bad input or unexpected conditions rather than broken components. Systems that were designed and systems that evolved both qualify.

Software engineers use it for programs that keep working whatever is thrown at them: malformed files, careless users, conditions nobody planned for. A robust program handles invalid input and edge cases gracefully instead of crashing or producing wrong output. Robust code is the everyday phrase, and it is praise for defensive design rather than for speed or elegance.

Strength of mind rather than of body. In practice it attaches as readily to what a mind produces as to the mind itself: robust findings, a robust proof, a robust explanation, a robust lesson. Said of a proof or a finding, it praises a plainness that uncertainty does not shake. Keep it apart from the statistician's technical term, which has a much narrower meaning.

One half of a specialist's pair: anthropologists, zoologists and paleontologists set robust against gracile, the slighter, more lightly built form. It applies to a whole individual or to a single skeletal element, so one bone can be called robust on its own. Unlike the everyday strong-and-healthy meaning, it says nothing about health, only about build.

A statistician's compliment for a method, not for a result. A robust estimator or test stays valid when the assumptions about the error distribution are wrong, for instance when the data depart from normality or outliers pull at the sample. Robust does not mean the answer is correct. It means the method does not hinge on one fragile assumption, which is a stricter claim than robust findings in everyday use.

A polite cover for rough play. Phil McNulty, reporting Everton against Liverpool for BBC Sport in 2011, calls Cahill's approach robust, and what he means is that it had already annoyed Jamie Carragher. The euphemism lets a writer signal rough or rude conduct without making a direct accusation. Read it that way when it describes behavior, and use it knowing listeners will hear the criticism underneath.