背・脊|せse[1]atamadaka (head-high)

1. nounback
   首くびや背せに太陽たいようが暑あつく照てりつけた。↗

   The sun beat down on our necks and backs.
2. nounreverse; rear side; back (e.g. of a chair); spine (of a book)
   彼かれはいすの背せにもたれている。↗

   He is leaning on the back of the chair.

   彼かれらは絶景ぜっけいを背せにして立たった。↗

   They stood against the picturesque scenery.
3. nounheight; stature
   トムはジャックと背せが同おなじくらいだ。↗

   Tom is as tall as Jack.
4. nounridge (of a mountain)

• Synonym背中せなかNeutralThe everyday word for the back as a body part. 「背」 also covers height, as in 「背が高い」, which 「背中」 does not.
• Synonym背面はいめんNeutralThe back or rear surface of a thing, as in 「建物の背面」; anatomy also speaks of 「人体の背面」. Never means height.
• SynonymバックCasualColloquial loanword covering the rear, a background, or backing support, as in 「バックに大物がいる」.
• Synonym背部はいぶWrittenMedical and formal term for the back, as in 「背部の痛み」. In everyday speech say 「背中」.
• Related後ろうしろNeutralThe direction or position behind, as in 「後ろを振り向く」. It points to a location, not a body part.
• Related後あとNeutralAlso covers the space behind one, out of sight, as in 「後ろから声をかける」.
• Related裏面りめんWrittenA written term for the reverse of paper or an object, or the hidden side of a matter, as in 「裏面工作」.
• Related裏うらNeutralThe reverse or back, also a hidden side, as in 「裏話」; the counterpart of 「表」.
• Related背後はいごWrittenBehind someone or behind the scenes, as in 「背後に回る」 and 「事件の背後」; leans toward written prose.
• Related後方こうほうWrittenAn archaic word for the rear; read 「しりえ」, it appears mainly in classical texts and is rare today.
• Related裏側うらがわNeutralThe side opposite the front or surface, also the inside story, as in 「月の裏側」 and 「業界の裏側」.
• Related後部こうぶWrittenA written term for the rear of a vehicle or object, as in 「車の後部座席」; mostly used of vehicles.
• Related裏手うらてNeutralThe area behind a building, as in 「店の裏手」; stresses the space at the rear of a house.
• Related後ろ側うしろがわNeutralThe side facing backward, as in 「家の後ろ側」; stresses direction and which side.
• Related後尾こうびWrittenA written term for the very end of a line, as in 「列の後尾」; mostly for queues and processions.
• Related後面こうめんWrittenWritten term for the rear of an object, as in 「後面図」; mostly seen on drawings.
• Related後背こうはいWrittenWritten term for the area behind or to the rear, as in 「後背地」; mostly in geography.
• Antonym腹はらNeutralThe opposite of 「背」: the belly at the front of the body; also one's mind or true intentions.
• Antonym面おもてWrittenOpposite of 「背」 in its reverse-side sense: the front or surface; leans written/formal.

Use 「背」 for the back and for height (「背が高い」); for the body part in everyday speech, 「背中」 is the usual word, while 「背部」 is medical and formal. For position behind, say 「後ろ」; for the rear surface of a thing, 「背面」 or 「裏側」; for behind the scenes, 「背後」; for the rear of a vehicle, 「後部」. The belly is 「腹」.

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

1. 背中せなか。胴どうの後ろ側うしろがわのうち、腰こしより頭あたまに近ちかい部分ぶぶん。胸むねと腹はらの反対はんたい側がわ。
2. ものを人ひとや動物どうぶつ（の胴どう）に見立みたてたときの背中せなかに当あたる部分ぶぶん。刃はの切きれない方ほうの縁えん。
3. 服ふくや道具どうぐの中なかで、人ひとの背中せなかに接せっする部分ぶぶん。
4. 身長しんちょう。