Daijr, ＫＯＤ追加語彙
アヒル口	12721
あひるぐち	326
あひるくち	32
家鴨口	106
あひる口	2277
アヒルグチ	53
アヒルクチ	< 20
アヒルくち	127
アヒルぐち	498

Whew. Daijr has アヒルくち, but it's less common.

@@ -6,0 +7,14 @@
+<k_ele>
+<keb>あひる口</keb>
+</k_ele>
+<k_ele>
+<keb>家鴨口</keb>
+</k_ele>
+<r_ele>
+<reb>アヒルぐち</reb>
+<re_restr>アヒル口</re_restr>
+</r_ele>
+<r_ele>
+<reb>アヒルくち</reb>
+<re_restr>アヒル口</re_restr>
+</r_ele>
@@ -8,0 +23,2 @@
+<re_restr>あひる口</re_restr>
+<re_restr>家鴨口</re_restr>
@@ -11,0 +28,10 @@
+<re_restr>あひる口</re_restr>
+<re_restr>家鴨口</re_restr>
+</r_ele>
+<r_ele>
+<reb>アヒルグチ</reb>
+<re_nokanji/>
+</r_ele>
+<r_ele>
+<reb>アヒルクチ</reb>
+<re_nokanji/>
@@ -15 +41,3 @@
-<gloss>duck face, a facial expression where the lips are pursed and corners of the mouth raised</gloss>
+<gloss>duck face</gloss>
+<gloss>duck lips</gloss>
+<gloss g_type="expl">facial expression where the lips are pursed and corners of the mouth raised</gloss>

https://ja.wikipedia.org/wiki/アヒル口
https://youtu.be/ZoiXnPfFQSw?t=25
https://www.google.com/search?q=アヒル口&tbm=isch

I wanted to add that the literal meaning is [lit] duck mouth, but I can't get it to work, the parser throws an error. :(