na-adjective, noun
Describes a person's unyielding, strong-willed nature; often used in a negative sense of being unreasonably stubborn. Can also imply a kind of tough-mindedness.
彼の剛腹な態度には手を焼いている。
I'm at my wits' end with his stubborn attitude.
剛腹を張り通すのも考えものだ。
Sticking to your obstinacy isn't always wise.
頑固 is the most common word for stubbornness; 剛腹 is less frequent and carries a nuance of tough, unyielding spirit, sometimes with a slightly more literary or old-fashioned feel.
意地っ張り emphasizes being willful or contrary, often over small matters; 剛腹 suggests a deeper, more ingrained obstinacy.
Compound of 剛 (strong, firm) and 腹 (belly, mind), suggesting a 'firm belly/mind' i.e., an unyielding spirit. The exact historical derivation is uncertain.