One-Word Substitution

A definition is given and you supply the single word. You cannot memorise every word, but you can read most of them from their parts.

1. A person, by belief or occupation. -ist and -arian (altruist, egotist, vegetarian), -phile a lover of (bibliophile, Anglophile), -phobe one who fears (xenophobe), -cide a killer or killing (regicide, homicide).
2. A place or a collection. aviary (birds), apiary (bees), granary (grain), arsenal (weapons), archives (records), mint (coins), sanatorium (the sick).
3. Forms of rule, with `-cracy` and `-archy`. autocracy (one ruler with absolute power), democracy (the people), theocracy (priests, in the name of god), oligarchy (a small group), anarchy (no government at all), bureaucracy (officials).
4. A quality or a state. omni- all (omnipotent all-powerful, omniscient all-knowing, omnipresent everywhere), in- not (inevitable, incorrigible, invincible), posthumous (after death), postmortem (after death, of an examination).

The single most common mistake is confusing near pairs: illegible (cannot be read) against ineligible (not qualified); omnipotent against omniscient; credible (believable) against creditable (praiseworthy) against credulous (too ready to believe); literate against literal.

How to check: split the word and read the parts back. in + corrigible = not correctable, so "one who cannot be corrected" is right; "one who cannot be cured" would be incurable, a different word entirely.

Split the word: omni- all, in- not, -phile lover, -phobe fearer, -cide killing, -cracy rule, -archy government · watch the near pairs: illegible vs ineligible, omnipotent vs omniscient, credible vs creditable vs credulous

One word for "a person who cannot be corrected or reformed". Options: incurable / incorrigible / inevitable / invincible. → incorrigible. Sanity check: split each option. "In-curable" is not curable and belongs to illness; "in-evitable" is what cannot be avoided; "in-vincible" is what cannot be defeated; only "in-corrigible" contains "corrigible", meaning correctable, which is exactly the definition given.