“Phase out” and “phaseout” differ by grammatical function. Merriam-Webster records “phaseout” as the noun and “phase out” as the corresponding verb, with forms such as “phased out” and “phasing out.”
ReviewedEvidence1 sourceSectionEnglish Usage
Quick answer
Use “phase out” as the verb meaning to discontinue gradually; use “phaseout” as the noun for the gradual discontinuation.
Key details
Confusion Familyword-boundary
Rule Familynoun versus phrasal verb
Termsphaseout, phase out
Variant ScopeClosed “phaseout” is the noun; spaced “phase out” is the verb.
Further guidance
Core difference
Use one-word “phaseout” for the process/event as a noun; use two-word “phase out” for the action as a verb.
Fast Test
If the phrase can inflect as “phased out” or “phasing out,” you need the two-word verb.
Usage Boundary
Hyphenation and house style can vary in modifiers, but the core noun-versus-verb distinction should remain clear.
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.
“Lockdown” is the noun for an official restriction or state of restricted movement, while “lock down” is the corresponding phrasal verb. Sentence function determines the spacing.
“Touchdown” and “touch down” differ mainly by grammatical function. Cambridge records the closed form as a countable noun for landing and sports senses and the two-word form as a phrasal verb, including aircraft landing and rugby uses.
“Turn off” is the two-word phrasal verb for switching something off, leaving a road, or causing loss of interest. The corresponding noun appears as closed “turnoff” in American usage and also as hyphenated “turn-off” in Cambridge.
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.”
“Any more” can be a determiner for additional quantity and an adverb meaning “no longer.” Cambridge notes that the one-word adverb “anymore” is especially common in American English, while the determiner remains two words.
“Anyone” is one word when it means any person. “Any one” is written as two words when the construction refers to a single member of a larger set, including the common pattern “any one of …”.
