das Visier
sight
An aiming device on a firearm or optical device that enables precise aiming.
Der Sportschütze blickte konzentriert durch das Visier seines Gewehrs.
The sport shooter looked intently through the sight of his rifle.

sight / visor
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sight
An aiming device on a firearm or optical device that enables precise aiming.
Der Sportschütze blickte konzentriert durch das Visier seines Gewehrs.
The sport shooter looked intently through the sight of his rifle.

The two literal meanings of 'Visier' (sight/visor) can be distinguished well from context. If people are talking about weapons, targets, or shooting, it means the aiming device. If it's about helmets, armor, or motorcyclists, it means the face protection.
Der Jäger schaute durch das Visier seines Gewehrs.
The hunter looked through the sight of his rifle.
The expression 'jemanden oder etwas im Visier haben' (to have someone or something in one's sights) means that you are observing or pursuing a person or thing in a targeted way. The object of the observation is in the accusative.
Die Polizei hat die verdächtige Gruppe schon länger im Visier.
The police have had the suspicious group in their sights for some time.
The expression 'mit offenem Visier kämpfen' (to fight with an open visor) means that you act or argue honestly and without hidden intentions. It comes from the age of knights, when an open visor showed the face.
Sie ist bekannt dafür, in politischen Diskussionen mit offenem Visier zu kämpfen.
She is known for fighting openly in political discussions.
When 'Visier' refers to a helmet's visor, the typical verbs are 'hochklappen' (to flip up) and 'herunterklappen' (to flip down), describing the movement of the face protection.
Er klappte das Visier hoch, um etwas trinken zu können.
He flipped up the visor so he could drink something.
goal / destination / target
'das Ziel' and 'das Visier' are related when it comes to aiming or focused attention. 'Ziel' is what you shoot at, look at, or work toward. 'Visier' is actually the sight used to aim precisely with a weapon or device. In the expression 'jemanden oder etwas im Visier haben' (to have someone or something in your sights), it also means that you are strongly focused on someone or something, or are watching it. Learners may confuse the words because both have to do with aiming. The important point is: the Ziel is the point or result; the Visier helps with aiming or describes the focus.

Die Polizei hatte den Verdächtigen schon seit Wochen im Visier.
The police had had the suspect in their sights for weeks.
Beim Training traf Paul das Ziel erst nach mehreren Versuchen.
During training, Paul hit the target only after several attempts.