It is one word.
The word "hairbrush" is typically written as one word, not two.
"Homecooked" is typically written as one word.
The word "underfund" is typically written as one word.
It is one word.
Jackrabbit is typically written as one word.
"Groundwater" is typically written as one word.
"Westside" is typically written as one word.
"Teabag" is typically written as one word.
"Snowplowing" is typically written as one word.
"Skillset" is typically written as one word.
It is usually written as one word.
"Boomtown" is typically written as one word.