diff --git a/src/wp-includes/category-template.php b/src/wp-includes/category-template.php
index f2ed10895c..671d9bfeae 100644
--- a/src/wp-includes/category-template.php
+++ b/src/wp-includes/category-template.php
@@ -1200,20 +1200,19 @@ function tag_description( $tag = 0 ) {
  * Retrieve term description.
  *
  * @since 2.8.0
+ * @since 4.9.2 The `$taxonomy` parameter was deprecated.
  *
  * @param int $term Optional. Term ID. Will use global term ID by default.
- * @param string $taxonomy Optional taxonomy name. Defaults to 'post_tag'.
  * @return string Term description, available.
  */
-function term_description( $term = 0, $taxonomy = 'post_tag' ) {
+function term_description( $term = 0 ) {
 	if ( ! $term && ( is_tax() || is_tag() || is_category() ) ) {
 		$term = get_queried_object();
 		if ( $term ) {
-			$taxonomy = $term->taxonomy;
-			$term     = $term->term_id;
+			$term = $term->term_id;
 		}
 	}
-	$description = get_term_field( 'description', $term, $taxonomy );
+	$description = get_term_field( 'description', $term );
 	return is_wp_error( $description ) ? '' : $description;
 }
 
diff --git a/tests/phpunit/tests/category/categoryDescription.php b/tests/phpunit/tests/category/categoryDescription.php
new file mode 100644
index 0000000000..f54c65bb0d
--- /dev/null
+++ b/tests/phpunit/tests/category/categoryDescription.php
@@ -0,0 +1,78 @@
+<?php
+
+/**
+ * @group taxonomy
+ * @covers ::category_description
+ */
+class Tests_Category_CategoryDescription extends WP_UnitTestCase {
+	public function test_success_query_by_id() {
+		$description = 'Foo';
+		$c = self::factory()->category->create( array(
+			'description' => $description,
+		) );
+
+		$found = category_description( $c );
+		$expected = apply_filters( 'term_description', $description );
+
+		$this->assertSame( $expected, $found );
+	}
+
+	public function test_success_query_by_object() {
+		$description = 'Foo';
+		$c = self::factory()->category->create( array(
+			'description' => $description,
+			'slug'        => 'bar',
+		) );
+
+		$category = get_term( $c );
+
+		$found = category_description( $c );
+		$expected = apply_filters( 'term_description', $description );
+
+		$this->assertSame( $expected, $found );
+	}
+
+	/**
+	 * @ticket 42605
+	 * @ticket 42771
+	 */
+	public function test_should_return_description_for_term_from_another_taxonomy_on_primed_cache() {
+		register_taxonomy( 'wptests_tax', 'post' );
+
+		$description = 'Foo';
+
+		$t = self::factory()->term->create( array(
+			'taxonomy'    => 'wptests_tax',
+			'description' => $description,
+		) );
+
+		$term = get_term( $t );
+
+		$found = category_description( $t );
+		$expected = apply_filters( 'term_description', $description );
+
+		$this->assertSame( $expected, $found );
+	}
+
+	/**
+	 * @ticket 42605
+	 * @ticket 42771
+	 */
+	public function test_should_return_description_for_term_from_another_taxonomy_on_empty_cache() {
+		register_taxonomy( 'wptests_tax', 'post' );
+
+		$description = 'Foo';
+
+		$t = self::factory()->term->create( array(
+			'taxonomy'    => 'wptests_tax',
+			'description' => $description,
+		) );
+
+		clean_term_cache( $t );
+
+		$found = category_description( $t );
+		$expected = apply_filters( 'term_description', $description );
+
+		$this->assertSame( $expected, $found );
+	}
+}