die Stirn
forehead
The part of the face located above the eyebrows and below the hairline.
Er wischte sich mit dem Handrücken den Schweiß von der Stirn.
He wiped the sweat from his forehead with the back of his hand.

forehead
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forehead
The part of the face located above the eyebrows and below the hairline.
Er wischte sich mit dem Handrücken den Schweiß von der Stirn.
He wiped the sweat from his forehead with the back of his hand.

The idiom 'jemandem/etwas die Stirn bieten' (to stand up to someone/something) is a fixed construction. The person or thing being resisted is always in the dative.
Sie hat ihrem Chef mutig die Stirn geboten.
She bravely stood up to her boss.
'Die Stirn runzeln' (to furrow one's brow) is a fixed combination of the verb 'runzeln' (to wrinkle/furrow) and the accusative object 'die Stirn' (the forehead). It expresses thought, skepticism, or concern.
Er runzelte die Stirn und las die E-Mail noch einmal.
He furrowed his brow and read the email again.
In its literal meaning, 'Stirn' is often combined with actions. Typical phrases are 'sich den Schweiß von der Stirn wischen' (to wipe the sweat from one's forehead) or 'die Stirn in Falten legen' (to wrinkle/furrow one's brow).
Nach dem langen Lauf wischte er sich den Schweiß von der Stirn.
After the long run, he wiped the sweat from his forehead.
eyebrow
'die Stirn' and 'die Augenbraue' are both in the upper part of the face and can therefore be easy to confuse. 'Die Stirn' is the larger area of skin above the eyebrows up to the hairline. 'Die Augenbraue' is the hairy arch directly above the eye. When someone is thinking or skeptical, they may 'die Stirn runzeln' (furrow their brow); this creates wrinkles on the forehead. If you are talking about the hair above the eye, 'Augenbraue' is correct.

Nach dem Sturz hatte Tom eine kleine Wunde an der Stirn.
After the fall, Tom had a small wound on his forehead.
Maria zieht eine Augenbraue hoch, weil sie die Antwort seltsam findet.
Maria raises an eyebrow because she finds the answer strange.