容器|ようきyouki[1]atamadaka (head-high)

1. nouncontainer; receptacle; vessel; packaging
   これらの容器ようきは気密きみつになっている。↗

   These containers are airtight.

• Synonym入れ物いれものNeutralEveryday word for anything that holds things, as in 「入れ物に入れる」; more colloquial than 「容器」, which sounds formal and suits packaging and product contexts.
• Synonym器うつわNeutralRefers to bowls, dishes and tableware rather than containers in general; it also figuratively describes a person's capacity, as in 「器が大きい」.
• Synonym器物きぶつWrittenWritten word for implements and utensils, as in 「器物損壊」; used mainly in legal and archaeological contexts.
• Antonym中身なかみNeutralAs 「当て身」 (あてみ), a martial-arts strike to a vital point, not an opposite of 「容器」. The contents of a container are 「中身」 (なかみ), a different word.
• Antonym内容物ないようぶつWrittenThe things inside a container, as in 「内容物を確認」; a written word seen mostly on product labels, the opposite of 「容器」.

For a container, 「容器」 is the standard, somewhat formal choice (「保存容器」); in casual speech say 「入れ物」. Use 「器」 for bowls and tableware. For what's inside, say 「中身」, or 「内容物」 on product labels; 「当て身」 is a martial-arts term, not an opposite.

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

1. 物ものを入いれる器うつわ。