missing hyphen in 'in app'

Quick answer - when to hyphenate compound adjectives

Hyphenate a compound modifier when two or more words together describe a noun that immediately follows them. Don't hyphenate when the same words come after the noun. Exceptions: adverbs ending in -ly (no hyphen) and compounds shown as closed or open in dictionaries.

Before a noun → hyphenate: a well-known author; a 10-year plan; a long-term solution.
After a noun → no hyphen: the author is well known; the plan lasts 10 years.
No hyphen with -ly adverbs: a highly regarded scientist (not highly-regarded).
Numbers + units when used as modifiers → hyphen: a 3-inch margin; a 5-year-old child.

Core explanation: what a compound adjective is and why the hyphen matters

A compound adjective (or compound modifier) is two or more words that function together to describe a noun. Placing a hyphen between them signals to the reader that the words form a single unit and prevents misreading.

Example: "small business owner" can mean either "a small-business owner" (owner of a small company) or "a small business owner" (an owner who is small). The hyphen resolves that ambiguity.

Modifier before noun → usually hyphenate. Modifier after noun → usually don't.
Adverbs ending in -ly never take a hyphen with the following adjective.
Check dictionaries for compounds that have become one word (e.g., email) or are conventionally open/closed.

Practical hyphenation rules you can apply now

Use this short checklist when you encounter a suspect phrase: (1) Is the phrase directly before a noun? (2) Do the words act together to describe that noun? (3) Is there a number or unit? (4) Does the first word end in -ly? If yes to 1-3 and no to 4, hyphenate.

If a phrase still looks awkward, rewrite: move the modifier after the noun or use an of-phrase.

Before a noun → hyphenate: a ten-year contract; a well-known actor.
After a noun → no hyphen: the contract is ten years; the actor is well known.
Adverb (-ly) + adjective → no hyphen: a highly skilled pianist.
Numbers + units → hyphen: a 3-year warranty; a twenty-one-year-old intern.

Real usage and tone: formal vs casual writing

Formal writing (reports, resumes, academic papers) favors hyphens to avoid ambiguity. Casual messages often omit them, but short or potentially unclear modifiers still benefit from hyphenation, especially in subject lines, headlines, and CVs.

Formal: hyphenate ambiguous compounds for clarity.
Casual: omit when the meaning is obvious, but hyphenate short modifiers that could be misread.
When in doubt in a professional context, prefer the hyphen.

Common examples and compact example bank

Use these before/after pairs as quick templates when proofreading.

Wrong: I bought a second hand car.
Right: I bought a second-hand car.
Wrong: The well known singer performed on stage.
Right: The well-known singer performed on stage.
Work - Wrong: They proposed a state of the art design.
Right: They proposed a state-of-the-art design.
Work - Wrong: We need a 10 year budget.
Right: We need a 10-year budget.
School - Wrong: This extra curricular activity is optional.
Right: This extra-curricular activity is optional.
School - Wrong: Please submit the mid term report by Friday.
Right: Please submit the mid-term report by Friday.
Casual - Wrong: Got a brand new laptop yesterday!
Right: Got a brand-new laptop yesterday!
Wrong: This is a long lasting battery.
Right: This is a long-lasting battery.
Wrong: He is a small business owner.
Right: He is a small-business owner. (If you mean the owner of a small company.)
Wrong: She is an award winning scientist.
Right: She is an award-winning scientist.
Casual - Wrong: I found a second hand jacket at the sale.
Right: I found a second-hand jacket at the sale.
Wrong: She has a half eaten apple.
Right: She has a half-eaten apple.

Try your own sentence

Test the whole sentence rather than the phrase alone: context often makes the correct form obvious.

Fix your sentence: quick checks and rewrite templates

Run this 5-step checklist, then use one of the rewrites if you're still unsure.

Checklist: (1) Before a noun? (2) Words act together? (3) Number/unit present? (4) First word ends in -ly? (5) Listed in a dictionary?
If unsure, rewrite by moving the modifier after the noun or using of-phrasing.

Original: We need a long term solution. Fix 1: We need a long-term solution. Fix 2: We need a solution that will last a long time.
Original: She is an award winning scientist. Fix 1: She is an award-winning scientist. Fix 2: The scientist has won several awards.
Original: They launched a ten year initiative. Fix 1: They launched a ten-year initiative. Fix 2: The initiative will last ten years.
Original: small business owner. Fix: small-business owner OR owner of a small business.
Original: The 10 year-old child was excited. Fix: The 10-year-old child was excited. OR The child, who is 10 years old, was excited.

Spacing, dashes, and other typography gotchas

Use a hyphen (-) to link words in compound adjectives. Use an en dash for ranges or connections (2018-2020, New York-London). Use an em dash for breaks in thought. Don't add spaces around hyphens in compounds.

Hyphen (-): compound modifiers - 5-year plan, user-friendly interface.
En dash (-): ranges or connections - 2019-2020 season, London-Paris route.
Em dash (-): breaks in thought - He arrived late-no excuses.
No spaces around hyphens: long-term (not long - term).

Wrong: We have a 5 - year plan.
Right: We have a 5-year plan.
Wrong: The 2019 - 2020 season was busy.
Right: The 2019-2020 season was busy. (Use an en dash for ranges where supported.)

Memory tricks and quick tests to spot missing hyphens

Three fast checks to use while proofreading:

Move-It test: move the modifier after the noun. If the sentence still reads naturally, you usually don't need a hyphen (a well-known researcher → the researcher is well known).
-ly test: if the first word ends in -ly, do not hyphenate (a highly rated course).
Numbers-and-Units: hyphenate when numbers/units modify a noun before it (a 20-page report).

Similar mistakes and related punctuation issues

Writers commonly mix up hyphens with en dashes or forget that some compounds have become single words. Phrasal verbs used as modifiers usually take hyphens when attributive: a broken-down car; a well-thought-out plan.

Hyphen vs en dash vs em dash - learn and apply one rule for each.
Compound nouns may be hyphenated, open, or closed - check a dictionary and be consistent.
Phrasal verbs before nouns often require hyphens: a hand-me-down dress; a run-of-the-mill solution.

Wrong: This is a well known case.
Right: This is a well-known case.
Casual - Wrong: She has a hand me down dress.
Right: She has a hand-me-down dress.
Wrong/Style shift: Email me the file. (Some older guides used e-mail.) Follow your dictionary or style guide consistently.

FAQ

Do you hyphenate compound adjectives after the noun?

Generally no. Hyphens are used when the compound modifier comes before the noun. After the noun, write it open: a well-known author → the author is well known.

Is it "half eaten" or "half-eaten"?

"Half-eaten" is correct when the phrase modifies a noun before it (a half-eaten sandwich). After the noun, you can write "The sandwich is half eaten," though keeping the hyphen can aid clarity.

Should I hyphenate numbers like 10 year plan?

Yes: use a hyphen for number + unit used as an adjective before a noun: "10-year plan." When the number follows the noun, write "the plan is 10 years long."

Is "well known" always hyphenated?

"Well-known" is hyphenated when it precedes a noun (a well-known fact). When it follows a verb, do not hyphenate: "The fact is well known."

How do I decide when to hyphenate unusual compounds?

Use the Move-It test: move the modifier after the noun. If the meaning is clear without the hyphen, you usually don't need one. If the phrase reads as a single idea or could be misread, hyphenate. Check a dictionary or your chosen style guide and stay consistent.

Want a quick check of your sentence?

If you're still unsure, run the Move-It test or paste your sentence into a checker for an immediate suggestion. Use these rules and quick tests to catch missed hyphens and keep your writing clear and consistent.