Insomnia is defined as an ongoing inability to sleep or stay asleep.(noun)
When you have trouble falling asleep even though you are tired, this is an example of insomnia.
See insomnia in Webster's New World College Dictionary
Origin: L < insomnis, sleepless < in-, in- + somnus, sleep: see somnolent
See insomnia in American Heritage Dictionary 4
Origin: Latin īnsomnia
Origin: , from īnsomnis, sleepless
Origin: : in-, not; see in-1
Origin: + somnus, sleep; see swep- in Indo-European roots.
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