Compound nouns
Words can be combined to form compound nouns. These are very common, and new combinations are invented almost daily. They normally have two parts. The first part tells us what kind of object or person it is, or what its purpose is. The second part identifies the object or person in question. Compound nouns often have a meaning that is different, or more specific, than the two separate words.
First part: type or purposeSecond part: what or whoCompound tankdiningtabledining-table
You have noticed that the compound noun can be written either as a single word, as a word with a hyphen, or as two words. There are no clear rules about this. A good rule of thumb is to write the most common compound nouns as one word, and the others as two words.
