ＯＫ|オッケーokkee

1. interjection, noun, suru verb, transitive verb, intransitive verbOK; okay
   フルコースもあれば、サラダで軽かるいお食事しょくじもオーケー。↗

   You can eat a complete meal, or just go easy with our salad bar.
2. nounfine (without); not needed; unnecessary; all right

• Synonym許可きょかNeutralFormal granting of permission, usually by a superior or an authority to an individual, as in 「外出を許可する」; 「ＯＫ」 is casual and spoken.
• Synonym認可にんかFormalOfficial approval by a government body or agency, as in 「認可保育園」; administrative vocabulary, whereas 「ＯＫ」 is the casual spoken way to say something is approved.
• Synonym同意どういNeutralAgreeing with an opinion or consenting to something, as in 「手術に同意する」; more serious than 「ＯＫ」, common in writing and paperwork.
• Synonym是認ぜにんWrittenJudging something as right and endorsing it, as in 「現状を是認する」; leans written and suits formal argument. 「ＯＫ」 is just a casual yes.
• SynonymよろしいFormalThe polite form of 「いい」, as in 「よろしいですか」; means the same 'that's fine' but far more courteous than 「ＯＫ」.
• Synonym賛成さんせいNeutralBacking an opinion or proposal, as in 「提案に賛成する」; about support, whereas 「ＯＫ」 is about permission.
• Related許すゆるすNeutralAll-purpose native verb: to allow, but also to forgive, as in 「罪を許す」; 「ＯＫ」 has no sense of forgiveness.
• Related承認しょうにんNeutralFormal approval recognizing something as legitimate, as in 「予算を承認する」; weightier than a casual 「ＯＫ」.
• Related容認ようにんWrittenTolerating or accepting a demand or proposal, as in 「容認できない」; written in flavour, while 「ＯＫ」 works as a direct spoken yes.
• Related聞き届けるききとどけるWrittenGranting a request, typically a superior answering a subordinate's wish, as in 「願いを聞き届ける」; strongly literary.
• Related聞き入れるききいれるNeutralTaking in or acting on advice or a request, as in 「忠告を聞き入れる」; about accepting it, not declaring it OK.
• Related差し許すさしゆるすWrittenOld-fashioned way of saying to permit; rare today — say 「許す」 or 「許可する」 instead.
• Related諾ううべなうWrittenArchaic written word for assenting or nodding yes; almost never used now — say 「承知する」 or 「ＯＫ」.
• Related諒するりょうするWrittenWritten word for accepting something with an understanding of the circumstances, as in 「事情を諒する」; rare — say 「了解する」.
• Related認許にんきょWrittenWritten word for approval or permission; rare today — use 「許可」 or 「承認」.
• Antonym不可ふかNeutralNot allowed or unacceptable, and a failing grade, as in 「可・不可」; more formal than 「ＮＧ」, the opposite of 「ＯＫ」.
• AntonymＮＧエヌ・ジーCasualColloquial for 'no good', not allowed, and also a failed take, as in 「ＮＧ集」; the opposite of 「ＯＫ」 in the yes/no sense.

For a casual yes, 「ＯＫ」 is the word. For formal permission use 「許可」, for an organization's official approval 「承認」, and for a courteous 'that's fine' 「よろしい」. 「是認」「容認」 lean written, 「認許」「諒する」 are rare written words, and the old-fashioned 「差し許す」「諾う」 are hardly used today. 「同意」 and 「賛成」 are about agreeing or supporting, 「許す」 also means to forgive, and 「聞き届ける」「聞き入れる」 are about granting or heeding a request. The opposites are colloquial 「ＮＧ」 and the more formal 「不可」.

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

1. 良よい、承認しょうにんする、許可きょかするという意思いしを表あらわす言葉ことば。
2. あってもなくてもいい、必要ひつようでないという意味いみ。