Bath powder is often referred to as "salt," specifically when it comes to bath salts used for relaxation and skin benefits. Additionally, some may use "bowl" in the context of a bowl of bath powder or products. However, for a more direct term, "salt" is the most common four-letter word associated with bath powder.
Bath.
US Cities with 4 letters in their names: * Reno, Nevada * Bath, Maine * Erie, Pennsylvania * Lynn, Masssachusetts
A narrow valley with 4 letters is called a "rift."
A partial bath in a home is also sometimes called a half bath, or a 3/4 bath. A half bath has a sink and toilet, a 3/4 bath has a shower, sink, and toilet.
Isle
Dove or Crow
Sire
Pixie - which is actually 5 letters.
tree
D Day
gala
mend