“Mustache” and “moustache” are regional spellings of the same word for hair above the upper lip. The guide keeps the documented US/UK preference explicit.
ReviewedEvidence1 sourceSectionEnglish Usage
Quick answer
Use “mustache” in US spelling and “moustache” in mainly UK spelling.
Key details
Confusion Familyregional-variant
Rule Familyregional-usage
TermsMustache, Moustache
Variant ScopeCambridge marks “mustache” as the US spelling and “moustache” as mainly UK, for the same noun.
Further guidance
Core difference
Use “mustache” in US spelling and “moustache” in mainly UK spelling.
Style Boundary
Choose the form that matches the regional or house style of the document, and keep the choice consistent where both forms are acceptable.
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.
“Acknowledgment” and “acknowledgement” are accepted spellings of the same noun. The guide treats the choice as a documented spelling-variant issue rather than labeling either form universally wrong.
Cambridge gives “adviser” as a headword and documents “advisor” as an accepted alternative spelling. The guide treats the choice as a documented variant boundary rather than assuming that one form is universally incorrect.
Cambridge marks “afterward” as the US form and “afterwards” as mainly UK, with the same adverbial meaning. The guide treats the choice as a documented variant boundary rather than assuming that one form is universally incorrect.
“Airplane” and “aeroplane” refer to the same type of powered fixed-wing aircraft. Cambridge documents a regional naming preference rather than a technical distinction.
Cambridge labels “ardour” as UK and “ardor” as US for the same noun meaning great enthusiasm or love. This guide treats the choice as a documented spelling convention and does not invent a meaning difference between the variants.
Cambridge documents “artifact” as the US spelling and “artefact” as mainly UK. The guide preserves that regional spelling boundary without inventing a meaning difference.
