空・虚|からkara[0]heiban (flat)

1. no-adjectiveemptiness; being empty
   ほとんど空からなのでガソリンを入いれなくてはなりません。↗

   I need to put some gas in the car, as it's almost empty.
2. prefixnot carrying anything; unburdened; empty-handed
3. prefixdishonoured (bill, promise, etc.); false; no-show (reservation); put-on (cheeriness, courage, etc.); empty (compliments); insincere

• Synonym空虚くうきょWrittenWritten/formal prose. Emptiness with no substance, as in 「空虚な日々」; mostly about the mind or heart, while 「空」 is mainly about having nothing inside.
• Synonym空っぽからっぽCasualColloquial. Completely empty, as in 「財布が空っぽ」; stresses that nothing is left inside.
• Synonym虚しいむなしいNeutralNeutral adjective. Empty or futile in feeling, as in 「虚しい努力」; leans toward emotions, while 「空」 also covers false, worthless promises.
• Synonymがら空きがらあきCasualColloquial. A place or train car is nearly deserted, as in 「電車ががら空き」; also used of weak, unguarded defences.
• SynonymガラガラCasualColloquial onomatopoeia. Empty and echoing, as in 「店がガラガラ」; also a clattering sound or a raspy voice.
• SynonymすっからかんCasualColloquial and humorous. Nothing left at all, often broke, as in 「財布がすっからかん」.
• Related空白くうはくNeutralNeutral. A blank where something should be, as in 「空白を埋める」; typical of documents and stretches of time.
• Related空洞くうどうNeutralNeutral. A physical cavity, as in 「虫歯の空洞」; by extension, lacking substance, as in 「空洞化」.
• Related空きあきNeutralNeutral. A vacancy or free time, as in 「空き部屋」「空き時間」; focuses on usable spare space, while 「空」 stresses nothing inside.
• Related空疎くうそWrittenWritten/formal prose. Hollow and lacking substance, as in 「空疎な議論」; mostly said of arguments and speech.
• Related無人むじんNeutralNeutral. Without people where people would be, as in 「無人島」 or an unstaffed 「無人駅」; it concerns missing people, not missing contents.
• Related中空ちゅうくうWrittenWritten/formal and technical. Hollow inside or mid-air, as in 「中空構造」.
• Related空所くうしょWrittenWritten/formal prose. A blank space or gap, e.g. in a text; in everyday speech say 「空いている所」.
• Related虚うろWrittenWritten/formal prose. A hollow part, such as a hole in a tree; in daily speech say 「穴」 or 「空洞」.
• RelatedエンプティーNeutralNeutral loanword. Just 'empty'; seen mainly on gauges and displays, as in 「エンプティー表示」.
• Antonym実じつWrittenWritten/formal prose. Substance and truth, as in 「実がない」; the antonym of 「空」 in having substance versus being hollow.
• Antonym真しんNeutralNeutral. Truth and sincerity, as in 「誠を尽くす」; opposed to 「空」 as genuine versus false.

Use 「空」 for something having nothing inside, and for false or worthless things like 「空約束」. Say 「空っぽ」 colloquially for totally empty, 「がら空き」 or 「ガラガラ」 for deserted places, 「空き」 for vacancies and free time, and 「空虚」 or 「虚しい」 for inner emptiness.

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

1. （から）何なんもないこと。
2. （クウ　仏教ぶっきょう）万物ばんぶつは因縁いんねんによる仮かりの姿すがたであり実体じったいはないという概念がいねん。