The story
Formed due to a misinterpretation of Three Musketeers as a compound noun that includes the stem three rather than as a plurale tantum proper noun.
Etymology from Wiktionary, CC BY-SA 4.0.
Three Musketeer
Today it means: Any one of the Three Musketeers in Alexandre Dumas' novel of the same name, i.e. either Athos, Aramis, or Porthos. Full definition →