You give a dollar for a pencil. You give time to finish a puzzle. You give effort to learn.
That is cost. Today we learn four words.
“Cost,” “costly,” “costing,” and “costless.”
Each word shares the idea of what you give to get something. Each does a different job.
Parents and children can learn these words together. They help with money and choices.
What Does “Same Word, Different Forms” Mean?
One idea takes different shapes. The idea here is the price or sacrifice for something.
“Cost” is a noun. “The cost of the toy is ten dollars.” Price.
“Cost” is also a verb. “How much does this book cost?” Action.
“Costly” is an adjective. “A diamond ring is costly.” Expensive.
“Costing” is a verb part or noun. “This project is costing us time.” Verb part. “The costing of materials is tricky.” Process.
“Costless” is an adjective. “Smiling is a costless gift.” Free.
Same root. Different endings. Different jobs. The price or sacrifice stays.
Personal Pronouns Change Their Form
Pronouns change for grammar. “I” becomes “me.” “We” becomes “us.”
Our words change for role and description. “The cost is high.” Noun.
“It costs five dollars.” Verb. “Gold is costly.” Describes.
“This is costing me sleep.” Verb part. “A costless solution.” Describes.
Pronouns help us speak faster. Word families help us talk about value.
When children know these four words, they understand trade-offs.
From Verb to Noun to Adjective to Adverb – One Family, Many Words
“Cost” works as a noun. “The cost of milk went up.” Price.
“Cost” also works as a verb. “What does the ticket cost?” Action.
“Costly” is an adjective. “Mistakes can be costly in time and money.” Expensive.
“Costing” is a verb part. “The repair is costing us a lot.” Verb part (present continuous).
“Costing” can be a noun in business. “Costing is part of accounting.” Rare for kids.
“Costless” is an adjective. “A costless upgrade? That is rare.” Free.
We have the adverb “costly” same form or “costlily” (rare). Skip it.
Five members. “Cost” is noun or verb. The rest are adjectives or verb part.
One Root, Many Roles – How Words Grow from Actions to Qualities
The root “cost” comes from Latin “constare,” meaning to stand together or to be fixed. The price was fixed.
From that root, we add “-ly” to make an adjective. “Costly” means having a high cost.
We add “-ing” for the present continuous verb. “Costing” means the action of having a cost right now.
We add “-less” to make an adjective meaning without. “Costless” means without cost.
Help your child see this pattern. Cost is the price. Costly means expensive. Costing means adding up cost now. Costless means free.
Same Meaning, Different Jobs – Is It a Verb or a Noun?
Look at “cost” in a sentence. Ask: Is it a price? Or is it an action?
“The cost of the game is twenty dollars.” Price. Noun.
“How much does this game cost?” Action. Verb.
Same word. Two jobs. Context tells you.
Now look at “costly.” Always an adjective. “Owning a car can be costly.”
“Costing” is a verb part. “The vacation is costing us a month of saving.”
“Costless” is always an adjective. “A costless download? Check for viruses.”
Teach children to look at the endings. “-ly” adjective. “-ing” verb part. “-less” adjective meaning without.
“Cost” alone can be noun or verb.
Adjectives and Adverbs – When Do We Add -ly?
We do not add “-ly” to “cost” to make an adverb. “Costly” is already an adjective.
The adverb form of “costly” is “costlily,” but it is very rare. “She bought costlily.” Not used.
We do not add “-ly” to “costing” or “costless.”
For children, skip adverbs. Focus on the main words.
“Cost” for price or action. “Costly” for expensive. “Costing” for happening now. “Costless” for free.
Watch Out for Tricky Spelling Changes (Double Letters, y to i, and More)
Spelling here is very simple. No double letters. No y to i changes.
“Cost” adds “-ly” to make “costly.” Just add. Keep the “t.”
“Cost” adds “-ing” to make “costing.” Just add.
“Cost” adds “-less” to make “costless.” Just add.
No dropping. No vowel changes. Very clean.
The only note: “cost” is irregular. Past tense is “cost” (not “costed” in price meaning). “It cost ten dollars yesterday.”
For “costing,” you can use “costed” in accounting but not for prices. Keep simple: cost, cost, cost.
Practice with your child. Write “cost.” Add “ly.” You get “costly.” Add “ing.” You get “costing.” Add “less.” You get “costless.”
No tricks. Very clean.
Let’s Practice – Can You Choose the Right Form?
Try these sentences. Fill in the blank with cost, costly, costing, or costless.
What is the _____ of this backpack? (noun, price)
A mistake can be _____ in time and effort. (adjective, expensive)
The repairs are _____ a lot of money. (verb part with are)
A smile is a _____ gift. (adjective, free)
How much does a ticket to the zoo _____? (action verb)
The _____ of electricity has risen this year. (noun)
Losing your keys is a _____ mistake. (adjective)
This project is _____ us more time than we planned. (verb part)
Answers: 1 cost, 2 costly, 3 costing, 4 costless, 5 cost, 6 cost, 7 costly, 8 costing.
Number 3 uses “costing” with “are” for present continuous tense.
Number 4 uses “costless” to mean “free of charge.”
Tips for Parents – Help Your Child Learn Word Families in a Fun Way
Look at price tags. “What is the cost of this toy?”
Talk about costly things. “A car is costly. It needs gas and insurance too.”
Use “costing” in real time. “This puzzle is costing us ten minutes already.”
Find costless things. “Hugs are costless. Kind words are costless.”
Play a game. You name an item. Your child guesses if it is costly or costless.
“A diamond?” “Costly.” “A rock?” “Costless (unless it is special).”
Read a book about saving money. “Alexander, Who Used to Be Rich Last Sunday” is great.
Do not correct every mistake. If your child says “costed” for past tense, gently say “The past of cost is cost. ‘Yesterday it cost five dollars.’”
Celebrate when your child uses “costless.” That is a less common but beautiful word.
Explain that “cost” can mean more than money. “The cost of staying up late is feeling tired.” A cost can be time, effort, or happiness.
Tomorrow you will check the cost of groceries. You will decide if a new toy is too costly. You will see the minutes costing you while you wait. You will give a costless compliment.
Your child might say “Help is costless. I helped you.” You will feel proud.
Keep counting costs. Keep noticing costly choices. Keep tracking what something is costing. Keep giving costless kindness.
Your child will grow in language and in understanding value. Not everything costs money. The best things are often costless.
