腰（こし、koshi）
- waist/hip

The Japanese word 腰 こし primarily refers to the "lower back," "waist," or "hips." It encompasses the area of the body between the ribs and the upper legs. It can also refer to the strength or vitality associated with this region.

⚫︎ 腰が痛い。 Translation: My lower back hurts. ⚫︎ 彼は腰をひねった。 Translation: He twisted his waist (lower back). ⚫︎ 腰を据えて仕事をする。 Translation: To settle down and work (lit: to set one's 腰).

⚫︎ This word is commonly used in everyday conversation to describe physical sensations, injuries, or actions related to the lower back and waist area. ⚫︎ It's essential when talking about pain, discomfort, or problems with the lower back. ⚫︎ It can also be used in more figurative senses, like describing someone's stance or determination. ⚫︎ Pay attention to the context to understand the exact nuance.

⚫︎ Kanji: 腰 ⚫︎ Hiragana: こし (used when kanji isn't known or for emphasis) ⚫︎ Katakana: not typically used. ⚫︎ Okurigana: 腰 is a standalone word and typically doesn't have variations in okurigana in its most common usage.

⚫︎ 背中（せなか）: back (broader term, includes the lower back) ⚫︎ ウエスト: waist (loanword from English) ⚫︎ 尻（しり）: buttocks/hips (more specific than 腰, focuses on the area below) ⚫︎ 骨盤（こつばん）: pelvis (more anatomical term)

There aren't direct antonyms for 腰 in the same way that "hot" and "cold" are antonyms. However, words related to other parts of the body could be considered opposites in a general sense, like 頭（あたま）: head, which is at the opposite end of the body. Also, weakness could be used as an antonym in some cases.

最近、腰が重いんだ。 ・Translation: Recently, my lower back feels heavy. ・Explanation: This sentence describes a feeling of heaviness or stiffness in the lower back, a common complaint.

彼は腰を痛めて、しばらく安静にする必要がある。 ・Translation: He hurt his lower back and needs to rest for a while. ・Explanation: This sentence explains that someone has injured their lower back, requiring rest and recovery.

The etymology of 腰 is not precisely known. It is considered a native Japanese word (yamato kotoba). It is believed to have originated from the ancient Japanese language.