As The Day Is Long Meaning

(idiomatic, intensifier) Unceasingly; very; thoroughly; to a very high degree.

Example: c. 1598, William Shakespeare, Much Ado about Nothing, act 2, sc. 1:
  He shows me where the bachelors sit, and there live we as merry as the day is long.
1851, Nathaniel Hawthorne, The House of Seven Gables, ch. 21:
  And you shall do nothing but what you choose, and shall be as happy as the day is long.
1872, Mark Twain, Roughing It, ch. 54:
  They are quiet, peaceable, tractable, free from drunkenness, and they are as industrious as the day is long.
1906, Horatio Alger, Joe The Hotel Boy, ch. 4:
  "Oh, I don't think they would steal the box. Bart Andrews and Jack Thompson are as honest as the day is long."
2003, Brian Buckner and Sebastian Jones, Friends, season 9, ep. 17 The One with the Memorial Service:
  Monica: Alright, wait a second! Why would Ross tell everyone in your class that you are "as gay as the day is long"?
2004, G. Caulkin and B. Glanville, "Souness eyes move to take Duff back on board," Times Online (UK), 16 Oct. (retrieved 6 Sept. 2009):
  "He is direct, honest as the day is long, hard-working and a good lad to have around."