di·ur·na·tion \ˌdī(ˌ)ərˈnāshən\noun (-s) Etymology: Latin diurnus of the day, daily + English -ation (as in hibernation) — more at journal 1.: the habit of sleeping or being quiescent by day < the diurnation of bats > 2.: a daily recurrent fluctuation in an ecological community (as the vertical movement of plankton)