Four words.
It is used as one word.
no it is not an one word it is of two word
I think the word "ongoing" is only one word, but it has two syllables that are two separate words.
Hipbone is one word.
The word "hairbrush" is typically written as one word, not two.
One word, two syllables
It is one word.
one word
It is one word.
"Hardworking" is one word.
"Center line" is typically written as two words. However, in specific contexts, such as engineering or technical fields, it may occasionally be hyphenated as "center-line." It's best to follow the style guide relevant to your specific use case to ensure consistency.
Toenail is one word.