Cambridge records “start-up” with “startup” as an alternative noun/adjective form for a newly started business or related context. “Start up” is the two-word phrasal verb for beginning operation or starting a business, organization, vehicle, or engine.
ReviewedEvidence1 sourceSectionEnglish Usage
Quick answer
Use “start up” for the verb. For the noun/adjective, both “start-up” and “startup” are documented.
Key details
Confusion Familyword-boundary
Noun Variant Scopehyphenated start-up and closed startup are both documented noun/adjective forms
Rule Familyorthographic-boundary
Termsstartup, start-up, start up
Choose the right form
Decision table for Startup vs. Start-up vs. Start Up
If you mean / need
Use
Why
a new business or a noun/adjective about starting operations
start-up / startup
Both non-verb spellings are documented.
to begin operating or cause something to begin
start up
The phrasal verb is two words.
Further guidance
Core difference
Use two words for the action “start up”; use “start-up” or “startup” when the expression functions as a noun or adjective.
Fast Test
If it becomes “started up” or “starting up,” it is the two-word verb.
Variant Boundary
Cambridge explicitly records “start-up” and “startup” as alternatives, so house style can govern the non-verb spelling.
Sources and evidence
Sources are shown with the role they play in this guide. Historical or style-sensitive claims are kept within the evidence boundary described above.
Standard English writes “a lot” as two words for a large amount, number, frequency, or degree. “Alot” is a common misspelling in this sense; it should not be confused with the separate verb “allot.”
“Blackout” is the closed noun, while “black out” is the two-word phrasal verb. The verb can describe losing consciousness or obscuring/darkening something; the noun names the resulting event or state.
“Blowout” is a closed noun for several events or results, and Cambridge also records “blow-out” as a noun variant. “Blow out” is the two-word phrasal verb, including the sense of extinguishing a flame.
“Breakout” is a closed noun for an escape and an adjective in several established senses. Cambridge also documents “break-out” in modifier use. “Break out” is the two-word phrasal verb for meanings such as beginning suddenly or escaping.
“Breakthrough” is a closed noun for an important discovery or advance and can also modify a following noun. “Break through” is the two-word phrasal verb for forcing or moving through a barrier or threshold.
“Build up” is the two-word phrasal verb. For the noun, Cambridge records hyphenated “build-up,” while its American dictionary also records closed “buildup.” The noun spelling therefore has a documented regional/style variant rather than one universal form.
