バックbakku

1. nounback; rear
2. nounbackground; backdrop
   海うみをバックに記念きねん写真しゃしん撮とろうよ。↗

   Let's get a picture of us with the sea in the background.
3. nounbacking; support; backer; supporter
4. noun, suru verb, intransitive verbgoing backwards; reversing; backing up
   彼かれは車くるまをバックさせて車庫しゃこに入いれた。↗

   He backed his car into the garage.
5. nounreverse (gear)
6. noun, suru verb, transitive verbrefunding; returning (e.g. profits)
7. noun, sportsback (player)
8. nounbackstroke (swimming)
9. noun, sportsbackhand
   俺おれはバックで打うつ方かたが得意とくいだな。↗

   I have a strong backhand.
10. noundoggy style (sexual position)

• Synonym背後はいごWrittenWritten word for what lies behind, also behind the scenes as in 「事件の背後」, often hinting someone secretly pulls the strings; バック's backer sense is a patron backing you up.
• Synonym後ろうしろNeutralThe everyday default for the space behind you; バック can also mean the rear but leans toward background, backing and reversing.
• Synonym後あとNeutralThe same word 「後ろ」 as above: the side behind you, most natural in speech; バック can mean the rear too but leans toward background and backing.
• Synonym背面はいめんWrittenWritten word for the face of an object turned backward, also a thing's hidden side; technical in flavor, while バック does not single out a surface.
• Synonym後方こうほうWrittenRead 「しりえ」, an archaic word for the rear now almost confined to classical texts; in daily speech say 「後ろ」 or 「後方（こうほう）」.
• SynonymリアNeutralLoanword for the rear of vehicles or equipment, as in 「リアシート」「リアカメラ」, mostly the first element of compounds; never background or backing.
• SynonymバックグラウンドNeutralLoanword for the background of a scene or event and for a person's history, plus computer background processes; バック covers background but not personal history.
• Synonym裏面うらめんNeutralThe back of a sheet of paper or an object, also the inside story, as in 「裏面に記入」「政界の裏面」; in ordinary usage バック is not used for the reverse side of a page or form.
• Synonym裏手うらてNeutralThe back of a building or place, as in 「家の裏手」「駅の裏手」; strictly a location word, with no background or backing sense.
• Synonym裏側うらがわNeutralThe reverse or other side, or the inside story, as in 「月の裏側」「業界の裏側」; バック can mean behind-the-scenes backers, but is not the ordinary word for an object's reverse.
• Synonym背せNeutralThe spine or back, extending to height and a book's spine, as in 「背が高い」; バック has no height or stature sense.
• Synonym背部はいぶWrittenWritten word for the back of a person or animal, common in medicine and expository prose; everyday speech uses 「背中」, and バック is not body-specific.
• Related裏うらNeutralThe reverse or hidden side of something, as in 「裏口」「裏事情」; apart from jargon like a playing card's back, バック is not the everyday word for an object's reverse.
• Related後部こうぶWrittenWritten word for the rear section of vehicles, ships or buildings, as in 「後部座席」; バック rarely names a part like this.
• Related背中せなかNeutralMainly the back of a person or animal, as in 「背中を押す」, though it extends to the matching part of things seen as bodies; バック rarely means the body's back alone.
• Related後ろ側うしろがわNeutralThe side at the back, stressing position or direction against 「前側」; it has none of バック's background or backing senses.
• Related後尾こうびWrittenThe tail end of a line or column of vehicles, as in 「最後尾」「列の後尾」, stressing being last; no background sense.
• Related後景こうけいWrittenArt and theater term for scenery at the back of a painting or stage; for everyday background use 「背景」 or 「バック」.
• Related後面こうめんWrittenWritten word for the rear face of an object, the counterpart of 「前面」; rare today — say 「後ろ」 or 「背面」 in everyday speech.
• Related後背こうはいWrittenWritten word for behind or the rear, mostly used as a prefix as in 「後背地」; rarely stands alone — everyday speech says 「後ろ」.
• AntonymフロントNeutralThe front or fore side, also a hotel front desk; the opposite of バック in the front-versus-back position.
• Antonym前進ぜんしんNeutralMoving forward; the opposite of バック when it means reversing or backing up, and also used figuratively for progress.

Use 「バック」 for background, backing or reversing. For the space behind you, the everyday word is 「後ろ」; for behind the scenes, 「背後」; for the reverse side, 「裏」; for the rear of vehicles or equipment, 「リア」 or 「後部」. The front is 「フロント」.

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

1. 背中せなか、後うしろ。
2. 背景はいけい。また背景音楽はいけいおんがく。
3. 後援（する）こうえん、後援こうえん者しゃ、後ろ盾うしろだて。
4. 後退こうたいする。
5. 返還へんかんする。
6. バックストロークの略りゃく。背泳せおよぎ。
7. 後背位こうはいい。
8. 「雄鹿おじか」に関かんする語ごを構成こうせい。
9. 小型こがたの携帯けいたい物入ものいれ、バッグ。