Trimming a bit. Don't really have an English term.

@@ -17,2 +17,2 @@
-<gloss>dressing room (connected to a bathroom)</gloss>
-<gloss>vanity room</gloss>
+<gloss>bathroom antechamber</gloss>
+<gloss>dressing room</gloss>
@@ -20 +19,0 @@
-<gloss>powder room</gloss>

リフォーム用語集
google images , native informer
https://ja.hinative.com/questions/23410829

This and 洗面所 are commonly used for the part of the bathroom (or the antechamber to the bathroom if yu prefer) where you have a basin and a washing machine in a Japanese home. While sure, it is a changing room, this isn't what it'd normally be called in English, would it?

Based on Google images, I think this sense should lead. I think 洗面所 should be more o less aligned w this sense.

@@ -14,0 +15,7 @@
+<sense>
+<pos>&n;</pos>
+<gloss>dressing room (connected to a bathroom)</gloss>
+<gloss>vanity room</gloss>
+<gloss>sink area</gloss>
+<gloss>powder room</gloss>
+</sense>

daijr, koj

I think "dressing room" is misleading.

@@ -17,2 +17 @@
-<gloss>dressing room</gloss>
-<gloss>changing room</gloss>
+<gloss>changing room (at a bathhouse, swimming pool, etc.)</gloss>

chuujiten

Hmm, turns out "bathhouse" is actually an AmEng term for this for swimmers, though I suspect most would 
interpret it as its common literal meaning. Some of the J-Es also have "locker room" in school/gym contexts.

@@ -17,0 +18 @@
+<gloss>changing room</gloss>