Webster's Revised Unabridged Dictionary · 1913

Mardi gras

Mardi gras , noun

[French, literally, fat Tuesday.]

1.
The last day of Carnival; the Tuesday before Ash Wednesday (the beginning of Lent and fasting); Shrove Tuesday; -- in some cities a great day of carnival and merrymaking; in the United States it is especially associated with New Orleans.
2.
The series of festival events celebrated on Mardi Gras{1}.