酷|こくkoku[1]atamadaka (head-high)

1. na-adjective, nounsevere; harsh; stringent; rigorous; strict; unfair

• Synonym過酷かこくWrittenWritten/formal word for harsh conditions or environments, as in 「過酷な労働」; 「酷」 says a demand or treatment is too harsh on a person.
• Synonym厳しいきびしいNeutralThe broadest term: strict or severe, and also difficult. 「酷」 is mostly used as 「酷だ」, with a nuance of being cruelly excessive.
• Synonym手厳しいてきびしいNeutralHarsh, unsparing criticism or treatment; the focus is on a stern attitude toward people.
• Synonym酷烈こくれつWrittenWritten and fairly rare: extremely severe or intense, said of environments, punishments, persecution; stronger than 「酷」.
• Synonym手ひどいてひどいNeutralDescribes harsh methods that inflict heavy damage, as in 「手ひどい打撃」; the focus is on the harm done.
• SynonymこっぴどいCasualColloquial, often adverbial, meaning 'severely', as in 「こっぴどく叱られる」.
• Related険しいけわしいNeutralDescribes steep terrain, and by extension a stern expression or grim outlook; the focus is on steepness or tension.
• Antonym優やさNeutralAntonym: a prefix meaning gentle and caring, as in 「優男」; the opposite of harsh 「酷」.

Use 「酷」 when a demand or treatment is too cruel on someone, often as 「それは酷だ」. For harsh conditions say 「過酷」, for strictness 「厳しい」, for unsparing criticism 「手厳しい」; 「酷烈」 is written and stronger, 「手ひどい」 stresses the damage done, 「こっ酷い」 is colloquial.

Usage comparisons are AI-assisted and cross-checked by multiple models; for study reference only

1. 酷ひどい。厳きびしい。