This is the 14789th most frequent Russian word.
платя
"Платя" is the present participle of the verb "платить," meaning "paying" in English.
In this sentence, 'платяной' relates to clothes, as a part of a compound describing the rail in the closet typically used for hanging dresses.
Она висит в шкафу, под платяной штангой.
It hangs in the closet, under the dress rail.
Here, 'платяные' is an adjective derived from 'платье' (dress), meaning 'wardrobe' or 'pertaining to clothes'.
Эти платяные шкафы очень вместительны.
These wardrobe closets are very spacious.
The term 'платяную щётку' refers to a specific tool used for cleaning clothes and is a typical usage of the word in its descriptive form.