adjective: whole or entire (referring to time)
From Old English leof (dear, used as an intensifier) + lang (long). Ultimately from the Indo-European root gleubh- (to tear apart), which is also the source of cleve, glyph, clever, clove (garlic), cleave, dermatoglyphics, lief, and lubricious. Earliest documented use: 1450
Usage (from Wordsmith)
“Life goes on in their little yellow bubble, where everyone merrily agrees with each other, all the livelong day.”
Emma Cowing; Nicola in a Spin That is Turning Her Head; Daily Mail (London, UK); May 2, 2015.