Theory:

Compound words are words that are created by combing two or more words with different meanings, to form a new word.
Example:
i. Dining + room = Dining room
ii. Cup + cakes = Cupcakes
iii. Pop + corn = Popcorn
iv. Ice + cream = Ice cream
v. Full + moon = Full moon
Compound words are formed using:
  • Noun + Noun
  • Gerund + Noun
  • Noun + Verb
Let us look into each form in detail:
1.Noun + Noun: Nouns, as we already know are words used to identify any of a class of people, places, or things (common noun), or to name a particular one of these (proper noun).
Example:
i. Bed + room = Bedroom
ii. Police + man = Policeman
iii. Note + book = Notebook
iv. Home + work = Homework
v. Cell + phone = Cell phone
2. Gerund + Noun: Gerunds are verbs that end with "ing" and are used as nouns. For instance,
Swim + ing  = Swimming. Swimming is fun.
Example:
I. Swimming + pool = Swimming pool
ii. Dining + hall = Dining hall
iii. Visiting + card = Visiting card
iv. Passing + cloud = Passing cloud
v. Calling + bell = Calling bell
3. Noun + Verb: When names of words (nouns) combine with action words (verbs).
Example:
i. Rain + fall = Rainfall
ii. Hair + cut = Haircut
iii. Dish + wash = Dish wash
iv. Head + ache = Headache
v. Sun + rise = Sunrise