Hibernation

4 clues
Sleep mode?
Winter sleep
Deep winter sleep
Serious winter sleep
Similar answers:
Abomination
Acrossthenation
Adestination
Africannation
Africannations
Aggressornation
Alienation
Aliennation
Alternation
Anation
Anexaminationof
Antagoniststagnation
Antinationalist
Arenations
Assassination
Assignation
Augustanational
Backexamination
Balkannation
Barexaminations