The last day is the great day of the feast of tabernacles:

John 7:37 In the last day, that GREAT day of the feast, Jesus stood and cried, saying, If any man thirst, let him come unto me, and drink.

Judgment Day is also called a "great day" in these verses:

Jude 6 And the angels which kept not their first estate, but left their own habitation, he hath reserved in everlasting chains under darkness unto the judgment of the GREAT DAY.

And,

Revelation 6:17 For the GREAT DAY of his wrath is come; and who shall be able to stand?