堅固|けんごkengo[1]atamadaka (head-high)

1. na-adjective, nounsolid; strong; firm
   その市しの防御ぼうぎょは堅固けんごだ。↗

   The defenses of the city are strong.

• Synonym強固きょうこWrittenA written/formal word for something firm and unshakable, as in 「強固な意志」. It goes mostly with will and relationships, while 「堅固」 leans toward castles and buildings.
• Synonym頑丈がんじょうNeutralNeutral in register. Describes a thing or a body as sturdy and durable; common in everyday speech, with the emphasis on standing up to knocks and impacts.
• Synonym堅牢けんろうWrittenA written/formal word for buildings and implements that are solid and long-lasting; it leans more toward physical objects than 「堅固」 does.
• Related頑強がんきょうWrittenA written/formal word for tenacity, as in 「頑強な抵抗」. It stresses refusing to yield easily rather than physical solidity.
• Antonym脆弱ぜいじゃくWrittenA written/formal antonym for things fragile and easily damaged, as in 「脆弱性」. It stands opposite to 「堅固」 in its solid, hard-to-break sense.
• AntonymもろいNeutralA neutral antonym covering brittle things and a soft heart. It opposes the firm, unyielding side of 「堅固」 and is common in everyday speech.

Use 「堅固」 for castles and buildings that are hard to break through, as in 「堅固な城」. For willpower either works — 「意志堅固」 is a set phrase, but 「強固な意志」 is the usual choice. Say 「頑丈」 for sturdy objects or bodies; antonyms are 「脆弱」 and 「脆い」.

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

1. しっかりしていて壊こわれにくいこと。
2. 意志いしが固かたく誘惑ゆうわくに負まけないこと。
3. 健康けんこうなこと。
4. 全まったく。まるで。
5. 絶対ぜったい。