diff --git a/eo-runtime/src/main/eo/ms/acos.eo b/eo-runtime/src/main/eo/ms/acos.eo
new file mode 100644
index 00000000000..3d42604944b
--- /dev/null
+++ b/eo-runtime/src/main/eo/ms/acos.eo
@@ -0,0 +1,78 @@
++alias ms.abs
++alias ms.pi
++alias ms.real
++architect yegor256@gmail.com
++home https://github.com/objectionary/eo
++package ms
++rt jvm org.eolang:eo-runtime:0.0.0
++rt node eo2js-runtime:0.0.0
++version 0.0.0
++spdx SPDX-FileCopyrightText: Copyright (c) 2016-2026 Objectionary.com
++spdx SPDX-License-Identifier: MIT
+
+# Calculates arc cosine of a `num` as `org.eolang.number`.
+[num] > acos ?
+  # Tests that arccosine of -1 equals pi.
+  [] +> tests-arccos-negative-one-test
+    eq. +> @
+      acos -1.0
+      pi
+
+  # Tests that arccosine of 0 equals pi/2.
+  [] +> tests-arccos-zero-test
+    eq. +> @
+      acos 0
+      div.
+        pi
+        2
+
+  # Tests that arccosine of 1 equals zero.
+  [] +> tests-arccos-one-test
+    eq. +> @
+      acos 1.0
+      0
+
+  # Tests acos calculation for a positive value inside [-1,1].
+  [] +> tests-arccos-positive-calculated-test
+    lt. +> @
+      abs
+        real
+          minus.
+            acos 0.6
+            0.927295
+      0.000001
+
+  # Tests acos calculation for a negative value inside [-1,1].
+  [] +> tests-arccos-negative-calculated-test
+    lt. +> @
+      abs
+        real
+          minus.
+            acos -0.6
+            2.214297
+      0.000001
+
+  # Tests that acos returns NaN for a positive value outside [-1,1].
+  [] +> tests-arccos-nan-positive-value-test
+    is-nan. +> @
+      acos 2.0
+
+  # Tests that acos returns NaN for a negative value outside [-1,1].
+  [] +> tests-arccos-nan-negative-value-test
+    is-nan. +> @
+      acos -2.0
+
+  # Tests that arccosine of NaN is NaN.
+  [] +> tests-arccos-nan-input
+    is-nan. +> @
+      acos nan
+
+  # Tests that arccosine of positive-infinity is NaN.
+  [] +> tests-arccos-positive-infinity
+    is-nan. +> @
+      acos positive-infinity
+
+  # Tests that arccosine of negative-infinity is NaN.
+  [] +> tests-arccos-negative-infinity
+    is-nan. +> @
+      acos negative-infinity
diff --git a/eo-runtime/src/main/eo/ms/real.eo b/eo-runtime/src/main/eo/ms/real.eo
index e171991fad2..3d510131ace 100644
--- a/eo-runtime/src/main/eo/ms/real.eo
+++ b/eo-runtime/src/main/eo/ms/real.eo
@@ -1,6 +1,5 @@
 +alias ms.abs
 +alias ms.e
-+alias ms.pi
 +alias ms.pow
 +architect yegor256@gmail.com
 +home https://github.com/objectionary/eo
@@ -30,13 +29,6 @@
   #  https://github.com/objectionary/eo/issues/4751
   [] > ln ?
 
-  # Calculates arc cosine of a `num` as `org.eolang.number`.
-  # @todo #4751:15min Move `acos` to a separate object with it's tests.
-  #  It's atom, don't forget change `EOreal$EOacos`.
-  #  For more information check this ticket:
-  #  https://github.com/objectionary/eo/issues/4751
-  [] > acos ?
-
   # Tests mathematical operation functionality.
   [] +> tests-positive-float-to-the-pow-of-positive-infinity-is-positive-infinity
     eq. +> @
@@ -210,59 +202,3 @@
       ln.
         real 20
       2.995732273553991
-
-  # Tests that arccosine of -1 equals pi.
-  [] +> tests-arccos-negative-one-test
-    eq. +> @
-      acos.
-        real -1.0
-      pi
-
-  # Tests that arccosine of 0 equals pi/2.
-  [] +> tests-arccos-zero-test
-    eq. +> @
-      acos.
-        real 0
-      div.
-        pi
-        2
-
-  # Tests that arccosine of 1 equals zero.
-  [] +> tests-arccos-one-test
-    eq. +> @
-      acos.
-        real 1.0
-      0
-
-  # Tests mathematical operation functionality.
-  [] +> tests-arccos-positive-calculated-test
-    lt. +> @
-      abs
-        real
-          minus.
-            acos.
-              real 0.6
-            0.927295
-      0.000001
-
-  # Tests mathematical operation functionality.
-  [] +> tests-arccos-negative-calculated-test
-    lt. +> @
-      abs
-        real
-          minus.
-            acos.
-              real -0.6
-            2.214297
-      0.000001
-
-  # Tests mathematical operation functionality.
-  [] +> tests-arccos-nan-positive-value-test
-    is-nan. +> @
-      acos.
-        real 2.0
-
-  # Tests mathematical operation functionality.
-  [] +> tests-arccos-nan-negative-value-test
-    is-nan. +> @
-      (real -2.0).acos
diff --git a/eo-runtime/src/main/java/org/eolang/EOms/EOreal$EOacos.java b/eo-runtime/src/main/java/org/eolang/EOms/EOacos.java
similarity index 58%
rename from eo-runtime/src/main/java/org/eolang/EOms/EOreal$EOacos.java
rename to eo-runtime/src/main/java/org/eolang/EOms/EOacos.java
index f99ba40afbc..d2721322c87 100644
--- a/eo-runtime/src/main/java/org/eolang/EOms/EOreal$EOacos.java
+++ b/eo-runtime/src/main/java/org/eolang/EOms/EOacos.java
@@ -9,6 +9,7 @@
  */
 package org.eolang.EOms; // NOPMD
 
+import org.eolang.AtVoid;
 import org.eolang.Atom;
 import org.eolang.Dataized;
 import org.eolang.PhDefault;
@@ -16,18 +17,25 @@
 import org.eolang.XmirObject;
 
 /**
- * Real.acos.
+ * Acos.
  *
  * @since 0.40
  * @checkstyle TypeNameCheck (100 lines)
  */
-@XmirObject(oname = "real.acos")
-@SuppressWarnings("PMD.AvoidDollarSigns")
-public final class EOreal$EOacos extends PhDefault implements Atom {
+@XmirObject(oname = "acos")
+public final class EOacos extends PhDefault implements Atom {
+    /**
+     * Ctor.
+     */
+    @SuppressWarnings("PMD.ConstructorOnlyInitializesOrCallOtherConstructors")
+    public EOacos() {
+        this.add("num", new AtVoid("num"));
+    }
+
     @Override
     public Phi lambda() {
         return new ToPhi(
-            Math.acos(new Dataized(this.take(Phi.RHO)).asNumber())
+            Math.acos(new Dataized(this.take("num")).asNumber())
         );
     }
 }