Compound nouns

A compound noun is a noun that is made up of two or more words. e.g. toothpaste

bedroom, raincoat, eyesight, dustbin, footstep, handbag, headquarters, notebook, postcard, rainbow

Compounds are sometimes written with a hyphen, as two separate words or as a single word. There are no clear rules.
ice-cream, ice cream, icecream

Compound nouns can also be formed using these word combinations:-

Noun + Noun (handbag)
Noun + Verb (sunset)

Adjective + Noun (weekly ticket)
Adjective + Verb (dry-cleaning)

Verb + Noun (sleep walker)

Preposition + Noun (underground)