I've found this book really helpful for a my genealogy projects:
https://www.amazon.com/Kriegsprache-Thomas-Houlihan/dp/05780...

And you can search it for terms online here:
https://tinyurl.com/ybsdr7ax

For "Schahrte" it lists: firing port, embrasure or loophole

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Note added at 2 hrs (2020-06-18 21:41:06 GMT)
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Scharte, sorry:-)

A couple of DE and EN references to back up Johanna’s posts:

"Der Durchbruch erfolgt rasch und am Mittag wird Mattstall erreicht, gegen 20 Uhr besetzten deutsche Truppen Woerth und Hagenau. Zum Schartenbeschuss wurde von der Wehrmacht die 3,7 Zentimeter PAK verwendet. Noch heute lassen sich in den Panzerkuppeln der Region die Spuren dieser Geschütze erkennen."
https://www.west-wall.de/index.php/maginot-linie/werke/das-f...

This is a Panzerkuppel and they have Scharten, as you can see in the pictures: https://de.wikipedia.org/wiki/Panzerkuppel

Another one:
“Die Sprenggranate ist die wichtigste Granate für m.Pz.Kpfw. Sie eignet sich zum Niederkämpfen von Zielen hinter Schutzschilden (Pz.Abwehr u. Art.) und lebende Ziele (vor allem Klächenziele). Bei letzterem von Abprallerschielten Gebrauch machen. Ziele hinter Deckungen können gefasst werden, außerdem eignet sie sich zum Schartenbeschuss der Bunker…Die Panzergranate findet ihre Verwendung gegen Panzerfeind. Feuereröffnung nicht über 800 m. Sie wird auch zum Schartenbeschuß von Bunkern eingesetzt.”
https://archive.org/stream/WaffenArsenalS33DerPanzerkampfwag...

Another three examples within one document:
“Nachdem ein Zug 8,8 cm Pak die Scharten eines Bunkers links der Straße zerschossen hat, wird dieser und anschließend ein zweiter Bunker rechts der Straße von den beiden vorn eingesetzten Kp. (9. u. 11.Kp. sowie Inf.Pi.Zug) genommen…Unter Verlusten gelingt es der 2. Kp. an der geschlossenen Scharte eines Bunkers geballte Ladungen anzulegen und zu sprengen…Ungeheuer war auch die Wirkung der Pak-Geschütze im Schartenbeschuss. Der Grundsatz des Rgt.Kdrs.: 'Schmeißt dem Gegner zuerst Eisen ins Gesicht - dann erst greift an unter ununterbrochenem Feuerschutz - und wenn die letzte Patrone drauf geht!' hatte sich erneut bewährt.”
https://www.forum-der-wehrmacht.de/index.php?thread/51302-de...

Similarly [p. 245]: "Die Bunker beiderseits der Eisenbahnbrücke über die Wolga wurden durch Schartenbeschuss zum Schweigen gebracht." https://ulis-buecherecke.ch/pdf_der_krieg/der_panzerkrieg.pd...

US sources related to WWII:
“Marine light tanks made brave frontal attacks against the fortifications, even firing their 37mm guns point blank into the embrasures, but they were inadequate for the task. One was lost to enemy fire, and the other two were withdrawn. Hays called for a section of 75mm halftracks. One was lost almost immediately, but the other used its heavier gun to considerable advantage.”
https://www.nps.gov/parkhistory/online_books/npswapa/extcont...

P. 25 shows a bunker with an embrasure:
https://luc.hawaii.gov/wp-content/uploads/2016/01/Appendix-E...

See also:
“Modern fortified areas -called ‘hedgehog’ -are characterized by concrete and steel pillboxes, steel turrets, open emplacements, troop shelters, slit-trenches and similar installations. Pillboxes form the heart of the defense system. They are camoufbged, rise only slightly above the ground, and are located so as to provide interlocking zones of fire and mutual fire support. In the pillboxes are weapons varying from machine guns to anti-tank guns up to light field artillery, and. the ground in front of the embrasures is leveled to assure long fields of fire.”
https://media.defense.gov/2011/Apr/20/2001330082/-1/-1/0/AFD...

Pillboxes: https://en.wikipedia.org/wiki/Pillbox_(military)

These pillboxes do have “Schießscharten”: https://de.wikipedia.org/wiki/Pillbox

And a photo taken in 1951 is described as follows: “Bazooka men, highly specialized and exactingly trained assault men, prepare to send a rocket explosive shell screaming into an embrasure of the ‘enemy’ concrete pillbox seen over the turret of the amphibious assault vehicle.”
https://www.trumanlibrary.gov/photograph-records/97-917

Plus:
“Private First Class Marvin Clevinger, Company B, Armored
Infantry Battalion, United States Army. For heroic achievement in connection with military operations against an enemy of the United States in Germany on March 26, 1945. During an attack on Schoden, Germany, an infantry platoon was suddenly pinned down by machine gun and sniper fire from a well-concealed pillbox. Private First Class Clevinger, scout, advanced 150 yards under the intense fire to within five yards of the enemy position from where he threw grenades through an embrasure in the pillbox, silencing the enemy fire.”
https://www.govinfo.gov/content/pkg/CREC-2011-06-23/html/CRE...

Same in the UK: “Type 23 pillbox, facing W. Large embrasures on three sides, and on the rear side is a splayed embrasure at the top of the elevation. Inside the open chamber is an AA mounting. Steps, with a safety rail, go down to the roofed chamber.”
https://heritage.suffolk.gov.uk/monument/MSF26338

It's even in M-W:
"2a: a protective embankment or dugout
especially : a fortified chamber mostly below ground often built of reinforced concrete and provided with embrasures"
https://www.merriam-webster.com/dictionary/bunker

In short, there is nothing wrong with the word embrasure.