diff --git a/poincare/Makefile b/poincare/Makefile
index 20a344f06..c7c104387 100644
--- a/poincare/Makefile
+++ b/poincare/Makefile
@@ -4,7 +4,7 @@ objs += $(addprefix poincare/src/,\
   binary_operation.o\
   commutative_operation.o\
   context.o\
-  cosinus.o\
+  cosine.o\
   expression.o\
   expression_lexer.o\
   expression_parser.o\
@@ -15,7 +15,7 @@ objs += $(addprefix poincare/src/,\
   leaf_expression.o\
   power.o\
   product.o\
-  sinus.o\
+  sine.o\
   subtraction.o\
   symbol.o\
   tangent.o\
diff --git a/poincare/include/poincare.h b/poincare/include/poincare.h
index 4b89926c0..21b774e7c 100644
--- a/poincare/include/poincare.h
+++ b/poincare/include/poincare.h
@@ -3,7 +3,7 @@
 
 #include <poincare/addition.h>
 #include <poincare/context.h>
-#include <poincare/cosinus.h>
+#include <poincare/cosine.h>
 #include <poincare/expression.h>
 #include <poincare/float.h>
 #include <poincare/fraction.h>
@@ -11,7 +11,7 @@
 #include <poincare/integer.h>
 #include <poincare/power.h>
 #include <poincare/product.h>
-#include <poincare/sinus.h>
+#include <poincare/sine.h>
 #include <poincare/subtraction.h>
 #include <poincare/symbol.h>
 #include <poincare/tangent.h>
diff --git a/poincare/include/poincare/cosine.h b/poincare/include/poincare/cosine.h
new file mode 100644
index 000000000..31f376375
--- /dev/null
+++ b/poincare/include/poincare/cosine.h
@@ -0,0 +1,14 @@
+#ifndef POINCARE_COSINE_H
+#define POINCARE_COSINE_H
+
+#include <poincare/function.h>
+
+class Cosine : public Function {
+  public:
+    Cosine(Expression * arg, bool clone_arg=true): Function(arg, (char*) "cos", clone_arg) {}
+    float approximate(Context& context) override;
+    Type type() override;
+    Expression * clone() override;
+};
+
+#endif
diff --git a/poincare/include/poincare/cosinus.h b/poincare/include/poincare/cosinus.h
deleted file mode 100644
index f23e66e4c..000000000
--- a/poincare/include/poincare/cosinus.h
+++ /dev/null
@@ -1,14 +0,0 @@
-#ifndef POINCARE_COSINUS_H
-#define POINCARE_COSINUS_H
-
-#include <poincare/function.h>
-
-class Cosinus : public Function {
-  public:
-    Cosinus(Expression * arg, bool clone_arg=true): Function(arg, (char*) "cos", clone_arg) {}
-    float approximate(Context& context) override;
-    Type type() override;
-    Expression * clone() override;
-};
-
-#endif
diff --git a/poincare/include/poincare/expression.h b/poincare/include/poincare/expression.h
index af5e199f5..a2d4946f4 100644
--- a/poincare/include/poincare/expression.h
+++ b/poincare/include/poincare/expression.h
@@ -10,13 +10,13 @@ class Expression {
   public:
     enum class Type : uint8_t {
       Addition,
-      Cosinus,
+      Cosine,
       Float,
       Fraction,
       Integer,
       Power,
       Product,
-      Sinus,
+      Sine,
       Subtraction,
       Symbol,
       Tangent,
diff --git a/poincare/include/poincare/sine.h b/poincare/include/poincare/sine.h
new file mode 100644
index 000000000..fe53563a0
--- /dev/null
+++ b/poincare/include/poincare/sine.h
@@ -0,0 +1,14 @@
+#ifndef POINCARE_SINE_H
+#define POINCARE_SINE_H
+
+#include <poincare/function.h>
+
+class Sine : public Function {
+  public:
+    Sine(Expression * arg, bool clone_arg=true): Function(arg, (char*) "sin", clone_arg) {}
+    float approximate(Context& context) override;
+    Type type() override;
+    Expression * clone() override;
+};
+
+#endif
diff --git a/poincare/include/poincare/sinus.h b/poincare/include/poincare/sinus.h
deleted file mode 100644
index a970aac09..000000000
--- a/poincare/include/poincare/sinus.h
+++ /dev/null
@@ -1,14 +0,0 @@
-#ifndef POINCARE_SINUS_H
-#define POINCARE_SINUS_H
-
-#include <poincare/function.h>
-
-class Sinus : public Function {
-  public:
-    Sinus(Expression * arg, bool clone_arg=true): Function(arg, (char*) "sin", clone_arg) {}
-    float approximate(Context& context) override;
-    Type type() override;
-    Expression * clone() override;
-};
-
-#endif
diff --git a/poincare/src/cosine.cpp b/poincare/src/cosine.cpp
new file mode 100644
index 000000000..8fafad923
--- /dev/null
+++ b/poincare/src/cosine.cpp
@@ -0,0 +1,15 @@
+#include <poincare/cosine.h>
+#include "layout/horizontal_layout.h"
+
+Expression * Cosine::clone() {
+  return new Cosine(m_arg, true);
+}
+
+Expression::Type Cosine::type() {
+  return Expression::Type::Cosine;
+}
+
+float Cosine::approximate(Context& context) {
+  // FIXME: use cosine obviously.
+  return m_arg->approximate(context);
+}
diff --git a/poincare/src/cosinus.cpp b/poincare/src/cosinus.cpp
deleted file mode 100644
index 070b82a2a..000000000
--- a/poincare/src/cosinus.cpp
+++ /dev/null
@@ -1,15 +0,0 @@
-#include <poincare/cosinus.h>
-#include "layout/horizontal_layout.h"
-
-Expression * Cosinus::clone() {
-  return new Cosinus(m_arg, true);
-}
-
-Expression::Type Cosinus::type() {
-  return Expression::Type::Cosinus;
-}
-
-float Cosinus::approximate(Context& context) {
-  // FIXME: use cosinus obviously.
-  return m_arg->approximate(context);
-}
diff --git a/poincare/src/expression_lexer.l b/poincare/src/expression_lexer.l
index 4a92ec02c..26a2dffdc 100644
--- a/poincare/src/expression_lexer.l
+++ b/poincare/src/expression_lexer.l
@@ -42,8 +42,8 @@ class Expression;
 %%
 
 [0-9]+ { yylval->string = yytext; return(INTEGER); }
-sin {return(SINUS);}
-cos {return(COSINUS);}
+sin {return(SINE);}
+cos {return(COSINE);}
 tan {return(TANGENT);}
 [A-Za-z]+ { yylval->string = yytext; return(SYMBOL); }
 \+ { return(PLUS); }
diff --git a/poincare/src/expression_parser.y b/poincare/src/expression_parser.y
index bb3dd2b14..43c501e64 100644
--- a/poincare/src/expression_parser.y
+++ b/poincare/src/expression_parser.y
@@ -54,8 +54,8 @@ void poincare_expression_yyerror(void * scanner, Expression ** expressionOutput,
 %token MULTIPLY
 %token DIVIDE
 %token POW
-%token SINUS
-%token COSINUS
+%token SINE
+%token COSINE
 %token TANGENT
 %token LEFT_PARENTHESIS
 %token RIGHT_PARENTHESIS
@@ -88,8 +88,8 @@ exp:
   | exp DIVIDE exp   { Expression * terms[2] = {$1,$3}; $$ = new Fraction(terms, false); }
   | exp POW exp      { Expression * terms[2] = {$1,$3}; $$ = new Power(terms, false); }
   | LEFT_PARENTHESIS exp RIGHT_PARENTHESIS     { $$ = $2; }
-  | SINUS LEFT_PARENTHESIS exp RIGHT_PARENTHESIS     { $$ = new Sinus($3); }
-  | COSINUS LEFT_PARENTHESIS exp RIGHT_PARENTHESIS     { $$ = new Cosinus($3); }
+  | SINE LEFT_PARENTHESIS exp RIGHT_PARENTHESIS     { $$ = new Sine($3); }
+  | COSINE LEFT_PARENTHESIS exp RIGHT_PARENTHESIS     { $$ = new Cosine($3); }
   | TANGENT LEFT_PARENTHESIS exp RIGHT_PARENTHESIS     { $$ = new Tangent($3); }
 ;
 
diff --git a/poincare/src/sine.cpp b/poincare/src/sine.cpp
new file mode 100644
index 000000000..fb3d7003c
--- /dev/null
+++ b/poincare/src/sine.cpp
@@ -0,0 +1,15 @@
+#include <poincare/sine.h>
+#include "layout/horizontal_layout.h"
+
+Expression * Sine::clone() {
+  return new Sine(m_arg, true);
+}
+
+Expression::Type Sine::type() {
+  return Expression::Type::Sine;
+}
+
+float Sine::approximate(Context& context) {
+  // FIXME: use sine obviously.
+  return m_arg->approximate(context);
+}
diff --git a/poincare/src/sinus.cpp b/poincare/src/sinus.cpp
deleted file mode 100644
index 9a73559a3..000000000
--- a/poincare/src/sinus.cpp
+++ /dev/null
@@ -1,15 +0,0 @@
-#include <poincare/sinus.h>
-#include "layout/horizontal_layout.h"
-
-Expression * Sinus::clone() {
-  return new Sinus(m_arg, true);
-}
-
-Expression::Type Sinus::type() {
-  return Expression::Type::Sinus;
-}
-
-float Sinus::approximate(Context& context) {
-  // FIXME: use sinus obviously.
-  return m_arg->approximate(context);
-}
diff --git a/poincare/test/trigo.cpp b/poincare/test/trigo.cpp
index 5878efbe1..700ac5b64 100644
--- a/poincare/test/trigo.cpp
+++ b/poincare/test/trigo.cpp
@@ -6,12 +6,12 @@ QUIZ_CASE(poincare_parse_trigo) {
   {
     Expression * e = Expression::parse("sin(0)");
     Expression * e2 = e->simplify();
-    assert(e2->type() == Expression::Type::Sinus);
+    assert(e2->type() == Expression::Type::Sine);
   }
   {
     Expression * e = Expression::parse("cos(0)");
     Expression * e2 = e->simplify();
-    assert(e2->type() == Expression::Type::Cosinus);
+    assert(e2->type() == Expression::Type::Cosine);
   }
   {
     Expression * e = Expression::parse("tan(0)");